Hi, well I am not familair with that game, so here are the questions/concerns:
What size are the maps? I am not sure if this is a render issue or a load issue. A faster CPU or faster video card might be more helpful if rendering is the key.
Are the maps coming from the HD, a CD, or the Internet? If either of the latter, can you pre-load onto a HDD?
Can you track your memory usage? Are you using a page file, or is everything fitting in the 1G? If the gane is using a page file, more memory or a second HDD dedicated for the page file would improve things.
I am assuming that you have XP Pro, so you should be able to monitor your resources if you don't have reasonable guesses to the answers to these questions.