I I have an old gx620 ultra small form factor that I'd like to upgrade because it fits PERFECTLY where it is and I haven't found any more modern unit that does. It has a pentium d820-2.8 ghz,800 mhz and I would like to go to a core 2 duo (e5200-e5800) if possible. I know it would FIT physically but would this mobo support it? I have a GATEWAY that can run both chips but I don't have a clue about the dell. I know it should run COOLER, and that should quiet it down- the fan runs hard and loud when it has to start working. If no on the e series then how high can I go on the pentium d series chips? I know the d945 would be a good bit quicker, but again, will this mobo support it? Thanx for any info you may have.I don't believe the Core 2 Duo chips are officially supported, though if you updated the BIOS to the latest it may work with the older Core 2 Duos such as the E6300 and E6600 Conroe CPUs.  The chipset should support them but Dell sometimes locks down CPU support in the BIOS.
The Pentium D chips aren't worth the money to upgrade to, they're all very slow compared to CPUs released in the last 6 YEARS or so unfortunately, so I wouldn't recommend spending money to upgrade to the 945.