In addition to what the last person told you:
Another option worth considering, but in the long run, probably not worth doing. I'll get to why not nearer the end of this post. Which ever way you choose to go, you should ensure that you have a backup. Also keep in mind that linux has a very different mind set to windows. (tip: avoid arguments with people over which OS is better😉 )
I've heard with mandrake linux (>8 I think) you can resize fat&NTFS partitions. I haven't tried this myself, but I've heard good reviews about it. I'm pretty sure I heard of this feature being in Redht 9 as well (this is what I use predominantly), I haven't seen this feature about, although I always do the partitioning manually so it ends up exactly as I want it.
I don't know if it's essential, but I wouldn't attempt resizing a partition without the partition being fully defraged first.
The following pros and cons apply to resizing with any util under any OS.
Reasons for resizing:
If you have a lot of "stuff" you don't want to backup because there's so much of it, but you do want to keep it. Resizing could be a good option. Keep in mind though, no matter what you are doing, no matter what OS, no matter what program ... etc if it is not backed up, you should expect to loose it at some stage.
Quick and convienient.
Reasons against resizing:
Any problems created during the process, may not show up until a lot later.
It's much "cleaner" to install from scratch.
Little gain over starting from scratch.
My Opinion:
I think in the long run, you'd be better off, going with the suggestions which the other person made (installing from scratch onto fresh partitions). My reasons are for my lack of trust for utils that mess with partitions. The risk of something going wrong is (in my opinion) greater than gain you will compared to starting from scratch.
So why did I write this post?:
Because this option commonly comes up in conversation, so the chances you are going to hear about it sometime soon if you haven't already (woa! De Ja Voo... I know I can't spell 😉 ).
On a different topic:
A good site to visit is:
http://linux-newbie.sunsite.dk/index.html
This site talks about when to and when not to consider linux, takes you through the various stages of getting it working and making it work well for what you want to do with it. It is a little out of date in places (about 2-3 versions in places). But there is some good info there.