The best way to clean a computer case if by blowing air and not vacuuming it imo. Much much better. Try and get a compressed canned air thingy. Should be fine for 3-4 thorough cleaning sessions... Not sure if there is any static build up in a plastic hose from a vacuum...Wouldn't worry much about it...
Static electricity is generated by particles (air, dust, dirt, etc.) being rubbed across the insides of the vacuum and what ever is really close to the nozzle.
As far as I know, there is no way to ground the vacuum cleaner.
While most recommend against using a vacuum to clean parts, I have been doing it for years with no issues.
Personally, I believe the risk of static shock to be quite overstated.
Much more of a concern is the risk that you will suck up jumpers, cables or other small parts.
Just be sure to take care when cleaning your system and you should have no issues.
I'd also suggest making sure you vacuum in a relatively humid environment. Dry air lets static electricity build up faster and stick around longer than normal air, so shut the door to your room and open up the windows for a few minutes before beginning to vacuum. That way, any air conditioned air will be replaced with more humid outside air.
I'm chocked how unknowing/ignorant some of you are:
EDS is the worst you can do to your computer !!! It's compared to welding on your electronic components - if you not destroy them immediately , they will suffer damages that can effect intermittent errors later on.
DON'T USE COMPRESSED AIR FOR CLEANING !!!
Use a vacuum-cleaner with a metal pipe and ground the pipe with some cupper-wire, don't get to close 6-10 as said before is OK.
Use a paintbrush to brush the dust of, and at all times use an grounding bracelet.