I've had to house rule grappling for old school games. The S&W solution for grappling left me... wanting more. The 3.X version of grappling left me.... wanting less. And do you really want to use those stupid tables from 2E? Even Gygax started fiddling with his original rules in 1E. So here's my solution. Poke holes at will.
When a character initiates a grapple, his player must state whether he is attempting to overbear or finesse the target into a grapple. If he is attempting to overbear the target, his Str score will be more important. If he is trying to finesse the target, his Dex score will be more important.
The target of the grapple then makes a saving throw, using the Str or Dex modifier of the initiating grappler as a bonus or penalty. If the initiator of the grapple is trying to overbear his opponent, his Str modifier is used to affect the final save value, and if he is trying to finesse the opponent, his Dex modifier is used in the same way. A positive modifier on the part of the initiator of the grapple is added to the number needed by the target to successfully save, making it more difficult. A negative modifier on the part of the initiator is subtracted from the number needed by the target to save, effectively making it easier.
For instance, if a character with a Str of 18 (+3) is attempting to overbear a character with a saving throw of 12, the character making the saving throw must roll 15 or higher (+3 from the initiating grappler's Str score is added to the saving throw of 12).
Also, if the target is a PC or NPC with ability scores (in other words, not a standard monster), his Str or Dex modifier, whichever he chooses, will apply to his saving throw. In the example above, if the target making the save had a Dex of 15 (+1 modifier), his +1 is applied to his saving throw roll.
If the target character saves successfully, he is not grappled. If the target character fails his saving throw, he gains the grappled condition. The initiating character is considered grapped also, but is also considered to have a hold. Characters who have a hold on a target impose an additional +2 penalty to the number needed by the target to break the grapple with a saving throw on subsequent rounds.
On the appropriate initiative phase of the next round, the target may attempt to break free from the grapple, which means another saving throw with all appropriate modifiers. The initiating grappler, if he still maintains his hold during the round, may choose to do his basic unarmed damage to the target or pin the character, which causes the target to be unable to move - he can still fight back and resist, but he cannot move. Certain other effects may be decided upon by the GM as he sees fit (such as a possible loss of Dex bonus), depending on the situation. A pinned character is not considered helpless, just severely restrained. Pinned characters may be tied up on subsequent rounds if the target does not break free. The GM can decide how he wants to handle tying a pinned character - another save may be called for, or a Dex check on the part of the character attempting to tie up the pinned character.
Note: to initiate a grapple, a character must close with his target and essentially step into the same space. If the initiating grappler closes with a target who is armed and attempts to grapple him, the target gets one free attack against the initiator as he closes to grapple, the result of which does not affect the grapple attempt unless the controlling player calls off the move.
Grappling with monsters poses a slight problem. They do not have ability scores and are often much larger than a regular PC. Monsters of higher power levels should be sufficiently difficult to grapple, as should large ones. Generally, the more powerful or larger a monster is, the more Hit Dice it has. Monsters use their HD as a modifier on their saving throws against being grappled, and as a modifier on their attempts to grapple PCs. For instance, a 5 HD monster attempts to grapple a character with a save of 12 and Str of 17 (+2). The monster imposes a +5 penalty to the save value, which means the character needs a 17 or higher to save against the grapple. He defending PC gets a +2 to his roll due to his Str.
As stated earlier, it also works in the reverse. Monsters use their HD as a bonus to their saving throw roll if they are the target of a grapple attempt. In the example above, the 5 HD monster, if he should be the target of a grapple, would get a +5 to his saving throw roll to avoid the grapple.
Using the HD of a monster as a bonus to the saving throw may seem weighted, but when you consider what it would actually take to wrestle a red dragon (basically a huge, smart, diabolical dinosaur), with 9-11 HD, it's not that far-fetched. It would be a difficult proposition at best, and probably doomed to failure. Smart men do not choose to wrestle dragons (or other beasts, for that matter), and most will take all precautions against becoming grabbed by one. Care must be taken by the GM, however, not to abuse this system of grappling with monsters - a 17 HD elemental that decides to grapple might want to have a good reason for choosing that option, since grappled characters need not break a grapple to make an attack.
Yes, I've implemented the use of Pathfinder's conditions into my game of S&W - like I told you, it is a Frankenstein monster of house rules. Here is the Grappled condition.
Grappled: A character in the midst of grappling is considered grappled. They are -4 to Dexterity, -2 on attack rolls except for rolls pertaining to the grappling contest, and must make successful Dexterity checks in order to cast spells. They can't complete actions that require two hands to complete, as at least one hand will be considered involved in fending off the other grappler.