Windows Vista Does compressing the hard drive where VISTA resides affect performance?

I am running low on space on my 70 Gig hard drive (18% free) where Vista resides and was wondering what affect, if any, compressing the drive would have on performance?

At what point does it make sense to compress any hard drive?

I have the same question about my XP PRO system and will post the question on that forum.

 

Did I mention VISTA was on my laptop?

Thanks, Steve, I appreciate your taking the time to respond.

I failed to mention that Vista was on my laptop which makes replacing it with a larger drive more difficult. But that is probably my best choice once I really hit a shortage.

I do have external hard drives that contain as many work directories as the programs will allow me to separate out. I and others wouldn't have these type problems if software vendors would quit putting data and work files in the program files directory and not giving users a choice on their locations. Until then we are forced to use whatever is available to conserve space and one of those is compressing the hard drive.

I was really hoping someone could quantity the performance loss, if any, with a compressed system drive.