My uncle has an AMD Duron 1.3ghz, the heating is insane. It was at 65C according to SpeedFan before I shut it down & clear out the dust, that only dropped it by 15C aprox.
Is there any suggestions rather than buy a new computer?
It's a HP computer so I can upgrade the case for more cooling options.

Duron's actually run very hot. Their critical temp is 90c.

You don't want to get anywhere NEAR that temp, but I'd say 65c (especially if that is under load) is nothing to worry about.

after he cleaned off the dust, he's now at 50c, which is even better

it's not worth buying a new case for a duron system, just keep what you have, your temps are fine.

Hmm, okay thanks.

yea buy a new proccesor and mobo

My Duron 950MHz started to be unstable over 50C. 0.18µM processors run hot.

I'd say put a nice heatsink in there and it should be OK. My Athlon XP 2000 runs at 35C idle, 52C load now, but I have LOTS of air blwing on it. (8" fan, CPU fan, exhaust fan)