The Inspiron 1501 can handle 2 X 1GB, so you are maxed out.  See this for additional info:

http://crucial.com/store/listparts.aspx?model=Inspiron%201501

Why only 2 GB if I can find 2 x 2GB of the same memory?

DMGrier

Amount of RAM supported is determined by the motherboard specifications.

Bev.

you can try 2x2gb, but make sure you can return it if it does not work.....but from what info i can gather, its 2gb max, and i checked 4 memory manufactuer,s..

memory support is determined by address bus, bios and chipset support.