Congrats! I just completed this upgrade last month and am enjoying the 7200rpm on a 100GB drive. WOW!
I'd encourage making a full backup of your current system & copying it onto the new drive. Preferably, you'd do this before the new drive is even installed. I'm not sure the network can handle such a task (I don't use my office netork for such hefty storage), but you can certainly accomplish this with an external drive.
Before writing off the external drive option, it might help to know that since you already have the new 7200 rpm drive, you can buy just a 2.5" Hard Drive Enclosure at any CompUsa or Best Buy for around $20. They're even cheaper online, but shipping often balances out the cost.
In that case, you'd just install the new drive into the enclosure, plug it into your system, and copy the image onto the new drive. (I've used Acronis TrueImage 9 for this, but you may have other options- I like Acronis b/c it manages details automatically, like accounting for a difference in source vs. destination disk size, partitioning, etc). Once that's complete, you just swap out the drives internally and you're ready to go. The enclosure can then be used with your OLD HDD as a backup drive, if you need it. If not, you can sell it to offset the cost of the new one.
Hope this helps.