I see that inshaala asked,

but if i can get it so windows runs off the 1gig pair, and photoshop of the
two gigs, i get more space then

A I understand the microsoft documents I cited earlier, you would need to
install 4 GBy in order to allow the application (e.g. Photoshop) to have
2GBy available. 

I see that gradient gave us a link on the Dell site,

http://support.dell.com/support/edocs/systems/dim5000/en/sm/parts0.htm

Which specifically says,

Your computer supports a maximum of 4 GB of memory when you use four
1-GB DIMMs. Current operating systems, such as Microsoft® Windows® XP,
can only use a maximum of 4 GB of address space

I checked one of my memory suppliers CoastMemory.com (AKA 18004memory.com) ... the memory configurator for a Dell Dimension 5000
specifically says (and they guarantee it) that the maximum expansion is
4GBy ... Dell Dimension 5000 expansion configuration

The price is $50 to $60 per memory stick.  (plus shipping ... about $40 for
2 day delivery).

If you can afford it, you should install 4GBy of the (faster) DIMM PC2-4200.

--
Martin