Not hard. Go to Dell.com. Click on search. Put in "Dimension 4500 users manual" (without the quotes). It should bring up 4 results from the Tech Support portion of their site. You should find some help there. HOWEVER, as was (sort of) mentioned you could have a major problem on your hands. As mentioned Dell does not use a standard ATX Power supply NOR motherboard. The mountings are different as are the I/O locations. IF you could get it in a standard ATX case you would kill it if you got it hooked to a standard Power Supply.
If by chance you managed to get another Dell case to put it in, you might be able to get it to work but it's a crap shoot. Sorry.