Right now my motherboard temp is sitting at about 23c and my cpu is idling at 75c. However, if I enter a cpu intensive program (games etc) it has risen to around 88c. I don't think it has hit 90 yet.

I really dont understand.

However, I am using the stock heatsink with the one fan mounted above the cpu. I've never had to face cooling before as my previous cpu was a 1.8ghz celeron.

I've been getting blue screen shutdowns non stop due to overheating so I went out and bought some thermal paste and applied it. I guess I lost a bit of temp as my pc actually booted into windows for a change (it would restart once everything in startup would finish). Not to mention I have the two sides of the case off and I have a big fan sitting on the outside blowing in on full power.

And by the way, at the moment I have a 3.4ghz pentium d. I've heard they get hot, but this isn't good.

Yes, they get pretty hot, but I don't think they're supposed to idle at 75c....

Adding more case fans might not work for you, because of the low m/b temperature.

Therefore, the easiest way to fix this would probably be to invest in an aftermarket CPU cooler. There are a variety out there, and some popular and good ones are the Zalman 9500, the Freezer7, and if you want something bigger, thermaltake Big Typhoon or the Tuniq Tower.

None of them would cost too much, and you'll see an immediate change in temps.

Also remember that you don't need alot of thermal paste. half a grain of rice in the middle of your CPU is adequate. If you've smeared it like peanut butter, thats way too much. This is dependent on your thermalpaste, but none should require you to smear it like peanut butter.

What sort of temperature drop would I be looking at?
And how hard would something like that be to install?
Is it powered by an area on the mobo etc?

Depending on which cooler.

All those coolers should be mobo-powered, using the same connection as your standard P4 cooler's fan.

You can expect at least 10C drop in temps. Your idle temps can go down as much as 35-40C. Dependent on the cooler you choose of course.

Installation wise, the smaller ones would be alot simpler to install, but the bigger ones are by no means impossible.

Anyways, there are tons of aftermarket coolers out there, don't assume they will perform as well as the short list like I've given you. That said, there are alot of aftermarket coolers out there which perform brilliantly, but not mentioned here as well. All you need to do would be to google that cooler, and look for a review which directly compares that cooler to one of those in my list. Those in the list are frequently used to compare new coolers to, and some other good ones they use would be the Zalman 9700, Scythe Ninja, and the Thermalright Ultra-120.

Just for closure, I did end up getting the Gigabyte one (wholesale) and my temp droppped from 80c idle to 28c idle.

Its running like a dream, thanks for the advice