I agree with DaveR. I have run XP with a variety of ram configurations ranging from 256 MB up to two gigs. 192 MB is seriously low for XP. Some folks who are extreme gamers, use serious cad programs, or do video editing need all the ram they can get for win XP, but as an ordinary user, I have found the point of diminishing returns for XP is about 512 MB, and after 756 MB of ram, I have see no benefits to be had with extra ram. This is not true for an OS like Vista with its better memory handling, and Vista will keep benefiting with every extra MB of ram installed. I assume Win7 will be similar to Vista, but can't speak from experience.
But Avast has one of the lower memory footprints for a active AV. Much leaner than McAfee. And if our OP is unwilling to upgrade to more ram, the alternative is to use msconfig to take seldom used programs off the start up list. Because as soon as the OS has to page to the hard disk and use it for virtual ram, its thousands as times slower than using actual ram. The other thing to mention is that even if I now have a spiffy fast dual core processor running Win XP, most of the times it feels no faster than older slower processors I used to have. Ram is and remains the number one speed booster for ram challenged XP computers.
And if our OP does want to add ram, please PM me because its an easy do it your self job. And to identify the type of ram you now have, there is an excellent freeware program called CPU-Z that will do just that.