I was mainly inquiring on memory in hopes of you having 128, 256 or 512mb of RAM. With 1gig, most things run pretty well in Windows XP with the exception of a couple games (such as BF2 or other memory-hog games).
On the memory discussion above, 32-bit operating systems can effectively see/use 4 gigs of address space. Of that 4 gigs, some is reserved for I/O address space & hardware address space. This is similar to the older 640KB limit with 1MB memory of DOS days- that extra 384KB is used for device address space. With 32-bit Windows, you can surely install 4gigs of RAM, but the OS will only see/have access to 4gig *minus* address space used by devices (i.e. usually 384MB to 1GIG depending on what cards/devices your system has). There are *tricks* to flip on additional real-time addressing (known a PAE), but I discourage this and it's only available on certain 64-bit capable CPU's. In general, stick with 3 gig, or add 4 gig (since it's cheap) but be prepared for Windows to only see 3.X of it due to address space reservation.
I guess the next real question would be- can you better describe how your computer is "slow at times" ? Where precisely is it slow and how does it illustrate this slow performance?
Off the top of my head, I'd also say try running a defrag on your disks as computers can operate very, very slowly if you've never done this.