Case fans - something good, quiet and dust-proof!

So I have a system that I've been using for a while now but I am looking to improve the airflow in my case a bit. Currently it has no case fans (it's a pretty old case) and relies just on my PSU sucking air out with a few empty PCI slots in the back for extra air movement. What I want to do is add a case fan at the front bottom of the case to pull some air in. One problem is that I get quite a lot of dust in my room so would need a good dust proof fan. Can anyone make any suggestions?

Thanks.

Rig:-
Gigabyte GA-P35-S3 Motherboard (rev 1.0)
Core2Duo E6600
Enermax Liberty 500W PSU
Crucial Ballistix 2GB DDR2 PC2-5300/667
WD 500G SATA2 WD5000AAKS HDD
EVGA GeForce 8800 GT 512MB Superclocked "Crysis Edition"

If you don't have an exhaust fan, add that first. If there is a lot of dust, about the only thing you can do is frequently clean up the inside of the computer.

I hate to bust your bubble, b u t y o u n e e d a n e w c a s e. I made that hard to read so you understand. Simple enough. You have a hot setup there and no case fans means your gonna let the smoke out soon. What are your temps in gaming on the CPU and GPU chips? **SHUDDERS** I'm really hoping you get the message.

Dust and a new case means you will have 3-6 120mm or larger fans blowing air. It's NOT dust proof. You WILL have to clean it up a bit every few months if you have any pride in your rig, half a can of dust off your good.

You got a nice system but like a nice car you need the right stuff, and ya gotta clean it.

Get an Antec 900 case, I have one and very happy. Or ask around for others.

Your gonna fry something.... It smells bad.

about the only way you're going to get dust proof is with watercooling. If it's worth it to you it might be a bad idea.

I live in Japan in a Tatami mat room. The mats are old and create a lot of dust. We also use a futon which is rolled out every night and stored everyday. So even more dust.
I have 2 rigs. One with an Xaser III Thermaltake case with loads of fans. The fans have dust covers. Although a tiny amount of dust still gets into the case through various small gaps - most of it sticks to the fan dust covers. Every 2 or 3 weeks I simply open her up and vacuum the covers.
(I also vacuum the GPU and CPU fans but I'm paranoid).

On the cheaper side..

The 2nd rig is junk. To help keep the HD drive in it cooler (by blowing air in) I untidily cut a square hole in the side removable metal panel, slightly smaller than an extra spare fan that came with one of my PSU's. I then drilled 4 holes inline with those on the fan and the fan simply sticks out as if stuck to the side of the panel. To stop dust - I use a very thin piece of cloth straight on top of the fan. Fold it over the fan sides and use rubber/elastic bands around the circumference to stretch it flat and keep it away from the fan itself. Not exactly Thermaltake - but it works like a charm and simply requires a vacuum nozzle up fairly close every month or so.
(3 or 4 elastic bands is a good idea to be on the safe side).

Where there's a will - there's a way.

Ok, sounds like I really need to replace my case. But I don't really want to spend loads. Can I get anything half good for around £50?