So, does that mean it doesn't have dust filters? If it doesn't, you can just go buy some at a store instead of using your mom's pantyhose lol.
Anyway, once you have dust filters, even if it's a dusty room just use compressed air to clean them off every few weeks, to keep airflow up (dust will plug it up, reducing air flow). Also if you can, keep the PC on a table instead of the floor.
Keep it off the floor, positive air pressure and compressed air every now and again is about the best you can do.
I knew someone once who set up a fancy air intake system using hoover tubes that drew air in from an air filtration machine, so no dust could get drawn from inside his room. From the little I remember, it worked well but cost a lot, and made his room cold! If you're innovative and have money to burn you could experiment with something like this, but you need to find some way to make sure there's enough air coming in to cool the system (because there'd be a reduced intake, you'd need to compensate by keeping the air moving quickly.)
Anyway, whatever you do, remember that it's something that affects mostly all gamers, so you're not on your own. I for one live in an old cob house, with my computer on the floor in my room, so dust for me is a real problem
I don't recommend dust filters, they work well at first, but eventually once they get clogged with dust, your airflow will die. So I recommend buying, a cheap HEPA air filter and putting it near your computer, in your room to keep the room itself dust free.
I have a nice quality honeywell HEPA airfilter and my computer is 99% dust free, well...my whole room is. I also try to keep positive pressure.
You will also breathe better, so its also good for health.