I'd look to set the swapfile minimum to 1GB, if it isn't at that already. XP shouldn't need any more than that really. Don't set a maximum. It might result in issues. I would recommend another 1GB of RAM, but on my XP system memory usage was never above 600MB or so, so wonder if it's more of a process/service issue.
Suggest you try CCleaner (recommended above) and get to the startup list and take a screendump, or list the startup processes. Most are probably good to be disabled for most users. 80% of my startup processes are disabled for no loss of functionality or security.
Run the program 'services.msc' and tweak the services columns (view, add/remove columns) so you have the name, status and startup type. Then Export as csv (Action, Export List, comma delimited).
With those two lists, you can tweak you system properly. I would suggest you post up both, but check that there's nothing sensitive in the lists before posting, such as private details (unlikely, but you never know).