As above - you need to remove files etc from your PC to make space for other stuff....
Now if you only have a diddy hard drive in the first place, and loads of stuff you don't want to lose, your best bet is to get a second storage device.....
Might I suggest this one?
http://www.pixmania.co.uk/uk/uk/3277...-3200-500.html
That is a fucking BARGAIN.... I paid nearer £80 last year for the same thing, cept mine was only 320gb!!!!
Lots of people slate Maxtor, but I'll let you into a little secret before they do - the drive inside is actually a Seagate barracuda drive! I know, cos when I got mine, I prised the case open, pulled out the drive and bunged it in my PC

But I then put the 80gb drive from my PC into the Maxtor case and still use it for storage and as a portable device.
It's a good bit of kit, well made and not let me down since I got it. And I still run the 320gb drive that came in it, in my PC aswell, which has also been faultless.....
Only trouble thing is it doesn't have an on/off switch, so rather than leave it on all the time, I just pulled the power plug out the back of it every night.....