|Go to www.crucial.com and use their scanner to tell what your options are for memory.|
Windows 7 32bit 'requires' 1GB RAM minimum but runs much better on 2-4GB (3.2GB max usable typically).
Windows 7 64bit 'requires' 2GB RAM minimum but runs much better on 4GB or more.
XP 32bit barely runs decent on 512MB RAM (especially with SP2 or SP3) depending on the programs you run and how you multitask. Even XP runs much better on 1-2GB.
I could not find any reference to your model number (especially without a brand name), but do the above scan and get as much as your system can take and you can afford (even 1GB will not cut it with Windows 7).
You have to be a little bit crazy to keep you from going insane.