Is there a hub, switch box or something that would let you use one moniter between two seperate computers? I am building a new system but buying the new moniter last. And I still need to use my old system and my new system at the same time. And it would be a pain to have to unscrew the moniter cables everytime.
Thanx in advance 
Yes, they do make them. You should be able to get a cheap one for about $20-30:
http://www.abra-electronics.com/catalog/computers/ds_614a.html
You’ll probably want to shop around for your own link if you can’t just pick one up locally. That’s the first link I found. Don’t expect the cheap one with mechanical pole switches to hold up for a lot of switching, but if you’re just using it until you spring for the second monitor, you’ll probably be OK. I have a similar little box hanging off one of my serial ports.
If you are choosing the monitor last a fair number of the better 19 and 21 inch monitors have switchable dual A/B input capability for either dual 15 pin VGA/VGA or VGA/BNC (which would require a VGA to BNC cable about $ 30 or so). This would have less signal loss and potential signal interference problems than a switchbox.