Hello
Long time listener, first time caller. I want to upgrade the CPU in my Dell PC, currently a Athlon x 2 4200. I would like to install an Athlon x2 6000 or 6400. CPU-Z states the PC has an AM2 socket. I will also upgrade the PSU (i found a specific unit for my PC from PC power & cooling). I know Dell makes upgrading a pain in the butt so my question(s) are. 1. Is it worth it or just a huge hassle? 2. Do i simply upgrade my BIOS from Dell and stick the new CPU in or does Dell specific BIOS make CPU upgrades a pain.

About all you can know for sure is that a CPU that the system originally shipped with will work. Otherwise, you can google around to see if someone else got a different CPU to work or just buy it and try it. I'd start with the Dell forums.

I believe that the fastest CPU originally offered with the E521 was a Windsor 5600+. Delluser1 would probably know for sure.

Being a Dell E521 owner I can say it won't happen.
X2 5600 Windsor would be it, provided you have the 89w cpu fan/heatsink and not the 65w.
I even spent 6 months looking for a X2 6000 89w till I found one.
Guess what?
No go, Dell was no help, and they don't care
Built my own
Couldn't be more pleased

The only other thing would be the oem X2 5400 Brisbane that Newegg had a while ago. I ran that with no issues.

OK, thanks a lot, I had a feeling that was the case

The X2 5400+ would be a nice bump from the X2 4200+. They're back down to $83 at the Egg.

Should be able to reuse your HSF is you have some AS5 goo laying around ...

You have to use the stock HSF btw