I certainly am glad you posted that screen shot. It changes things a bit. Microsoft wants to make it as difficult as possible to try something else. lol
You already have 3 partitions on the disk. sda1 is probably some kind of boot loader, sda2 is your Vista install, and sda3 is a Vista recovery partition.
I honestly don't know if it is safe to change the partition number of the recovery partition. I would hate to have you change it, which we would have to do if we set it up the way I had originally intended, and at some later date you need it to restore your Vista install and it didn't work. Not knowing how Vista handles that I hesitate to change it. If you haven't already figured it out, I tend to be rather conservative.
So, what we need to do is get your free space to the end of your partition table, which will leave the first 3 partitions numbered as they are, which is a bit beyond what the installer can do.
If you are willing to stick with it, I will walk you through the process. I like to think I am slow and thorough. Others might say slow and plodding. But we will get there. It really isn't that hard, just new to you.
For now I am going to assume you want to go on. First I want you to download a small Linux live cd called Puppy shard 3.01 iso. You will find it on the Puppy Linux community site. It came out in Nov. I believe. It isn't large, only about 155 MB. Burn it slow to a cd and check the md5 sum. When you are done put it in your drive and reboot. It runs completely in ram and won't touch your hard disk unless you tell it to. You will have to answer a few questions, language, keyboard, etc. Choose xorg when asked and you will get a nice simple Win98 like screen. Right click on the screen and you will get a menu. Under utilities you will see Gparted. Click on it and when the program opens you will see a graphical representation of your disk with the text about each partition in a table below it. Right click on one of the partitions and you will see an entry called resize/move. Choose that and you will see what that does. You pick the size you want and the space before or after the partition. You can poke around and familiarize yourself with the various options and screens. Don't actually commit anything, just look.
When you feel comfortable with what you see, close the program without committing anything.
Ok you can remove the cd and log out of Puppy and restart. When it asks you if you want to save the session choose "NO." Log back into Vista.
I always suggest that you defrag your hard drive before you shrink partitions. I think it just gives you a little more safety. Others will tell you it isn't needed, and they are probably right, but it just makes me feel more comfortable and also gives you a faster Vista when it is all over with. There is no iron clad guarantee that you won't loose data when you resize a partition, so anything you have that you absolutely can't afford to loose, back it up. Having said that I can tell you that people do it successfully everyday, but a warning is still in order. Ok go ahead and start the defrag if you wish to do so. It will take a while.
Ok lets decide how much space you are going to liberate from the Vista install. You are currently using 42.7 Gig. If we allow you 8 Gig. more for programs and data that would be 50.7 Gig. You need about 20% head room which would be another 10.1 Gig. for a total of 60.8 Gig. The partition is currently 74.9 Gig less the 60.8 Gig you want to keep gives us approximately 14 Gig. to work with. I wouldn't suggest you take anymore than that out of your Vista install.
With 14 Gig to work with lets see what we can do. How about swap=2 Gig., / (root)=8 Gig, and /home=4 Gig. That should give you plenty of space in /home for you to see if you like Mint. If you later decide to get another drive you can move /home to the new drive, or reinstall the whole installation there for that matter. You will have several options at that point.
I think thats enough for one bite.
Post back if this is the way you want to go or if you have other questions. And we can move on from there.