Not exactly, but depending on what kind of memory you mean there may be stuff you can do. If you're talking about actual space for storing stuff, on your hard drive, you're basically out of luck. If you're talking about RAM, which you probably are since that's the kind of memory thats likely to impact your operating speed, there may be stuff you can do
Basically you have a certain amount of RAM and a certain pagefile allocation on your hard drive, and your computer uses your pagefile allocation as virtual RAM when you spill over. By default your pagefile is normally set somewhere in the region of 1.5x the amount of RAM you have. Ideally you'll never use your pagefile allocation, because direct RAM access is quicker, but if you're not only using it but maxing it you may see a performance improvement by increasing your pagefile allocation creating more virtual memory.
To increase your pagefile, in XP go to control panel, system, advanced, settings, performance/advanced. I'd suggest setting it at 3x the amount of RAM you have. If you're not sure how much RAM you have, in control panel click on system and it'll be displayed.