Hey guys.
I have a Dell Dimension 8250 which I bought in 2002.
These days, it's having problems--it's freezing a lot. I don't know if it's a hot CPU, or VGA or hard drive. I think it's the CPU though. It is a socket 478 Pentium 4, 2.4Ghz, with a stock heatsink.
I am thinking of getting a good heatsink, but I don't know which are 'compatible' or not.
I was thinking about a Thermalright heatsink. But if any of you guys have experience installing a heatsink not bought from Dell, let me know what you guys recommend.
Thanks guys.

Before you go and buy a new HS try blowing some of the dust out with a can of compressed air or something, after you've cleared the dust build up then re-chek your temps.

Thanks for the tip. I've already done that, so maybe I should still get a new one? 8)
I have the stock HS that is like 5 bucks.

Next I'd borrow a temperature meter off someone to measure those heatsink temps. Or it can be easier just to touch the heatsink - if you cant comfortably keep your fingers on it for about 10 seconds then you know there's a heating issue there.

Reseating them with AS5 is another option too.

so, I have another question...

Is there a way I could unscrew the current retention module (for processor) and put in another one? (e.g., replace my socket-423's retention module for a socket-478 one so I could have more options with heatsinks.)

I'm not sure. you'd have to measure it all up to check whether the holes would be able to be cut in the right motherboard and the top of the CPUplaces, enough room, the clearance between the die must be the same or else the cooler isn't going to come into proper contact with the CPU.
Have fun