A lot depends on how much ram you have - If you have 512 mb or more, you only really need 1 gig max and then only if you are doing a lot of multitasking or working with LARGE picture files or video etc.
If you have 1gig or ram, I would set your swap file to 200mb just to stop windows complaining.
Your best bet would also be to set the minimum and maximum swap file to the same size - That way, you wont get a fragmented swap file and decreased performance.