are you using the latest bios?
the A31 bios fixed issues with Supporting DDR333(Run as DDR266) on Inspiron 5100.

Yes, I have Bios A32, I think that is the latest right now. So, my laptop is using PC2700, 333 MHz  as PC2100, 266 MHz? That is why it recognized it, cool....learn something new everyday. How can I test a memory module to see if it functioning properly or not?

What if one might have lost his original Dell software during a move, is it downloadable? I have sonic record, it makes bootable CDs, but always asks me for a floppy to use for the bootable source to copy?? Any answers for that? Good programs for making bootable CDs without a floppy drive?

you can run the dell diagnostics to check your memory.

it would have come on a cd called dell utilities and you'll have to boot from the cd to run the program.

Then you make a clone using an EZGIG kit or Travelstar upgrade kit. http://www.compusa.com/products/product_info.asp?ref=froogle&pfp=froogle&product_code=52063920

The travelstar kits include EZGIG.  If you have a drive you can just get the kit.

 

http://accessories.us.dell.com/sna/productdetail.aspx?sku=A0158183&cs=19&c=us&l=en