What to do with an old Dimension 4500

Both Dell and Crucial (a most popular memory supplier) state the max memory for this older model is 2 X 512 MB, so just because a module will "fit" doesn't mean it will work correctly and reliably.  If you want to try expanding the memory to 2 X 1 GB you can do so, as some have reported being able to go beyond the documented max, but at least use modules more likely to work, such as these from Crucial:

http://crucial.com/store/listparts.aspx?model=Dimension%204500%20Series#

Spending much money on this older model with processor upgrades and the like makes no sense with new computer models available for the $500's and up, all with warranty.  Check the Dell outlet for particularly good deals.