A couple more considerations, if I might.
If you plan to shrink your C: partition, it's probably worth thoroughly defragmenting it first - even if the Windows defrag tool tells you this is unnecessary. Not sure that the Sourceforge guide mentions that. I murdered an XP partition by shrinking it substantially, without first defragging.
Could easily have been something else, of course.
My old nemesis, the limited number of primary partitions possible, rears its head here. You can only have four primary partitions on one drive. (I used to think this applied across drives - luckily I was wrong - as wa pointed out here.)
If you plan to use a swap partition, then you're looking at adding at least two partitions to your present arrangement - /root and swap - giving a total of five partitions.
Fortunately, it would be a simple matter to create one extended partition in the space you plan to allocate Linux (guides available on line), and to create your root, home, swap and whatever else you want within that extended partition as individual logical partitions.
One of the few things I dislike about the Ubuntu series is the partitioning tool. Just the way my mind is wired, but I find it anything but intuitive - even when I've prepared partitions in advance with GParted.
Which I personally find simplifies installations.
A final suggestion. As a serial buyer of ancient laptops to mess around with, I get the impression that laptop manufacturers tend to bow and scrape to Microsoft, to the extent that their support for Linux is incredibly and disgracefully poor. (Just my own opinion, of course.)
I find it worthwhile burning a variety of CDs, and if one distro doesn't work on a particular computer, and can usually, with patience, find one that does cope with the hardware concerned. (One can usually find the necessary drivers eventually, but this only worth while if you find this sort of thing fun - which it can in fact be.)
Although Mint remains my preferred distro, I've found that a couple of laptops cope better with Mandriva and with Mepis. Ubuntu's commendable adherence to the avoidance of non-free drivers etc can involve a little more work than one might like, but at least there are perfectly legit ways and means, and lots of information available - just involves a little more work.
Mepis, incidentally, has the most unfriendly user-agreement I've seen in a Linux distro, but more than atones for this in its incredibly friendly and helpful forums. Wireless seems to be its weakness - if it doesn't work straight away, a certain amount of Colourful Language will ensue by the time it does - but it's a splendid distro, otherwise, and greatly overlooked.
Have fun, anyway. I find I feel more relaxed surfing from a Linux partition - although I do occasionally worry that I might have become a little complacent - so still use all the Firefox add-ons, and try to remember to think occasionally before clicking...