More memory 1st priority!!
Since you have a PIII, your still running SDRAM so go get yourself a brand new 512MB stick (buy a good brand name like Corsair or Kingston) & toss that puppy in. You'll need to check your motherboard specs to see which memory you should be using, if you don't have a manual or know the MB mfg, download Everest home edition, it'll tell you all about your PC.
Put the new stick of RAM in the 1st mem slot & put the 128MB you already have in the 2nd slot, if!! you can't boot or start getting errors BSOD or anything out of the ordinary happening yank the 128MB it likey isn't compatible with the new 512MB RAM.
Virtual memory, well you really don't want to use it, you want your system using the installed memory first because it's faster, however by upgrading the RAM alone it won't 100% solve the problem. You need to do two things, I'll suggest a couple other things also but there up to you whether you do them or not, there simple & will make your memory work for you......