By now you know that you can download the Windows 7 Release Candidate free of charge from Microsoft and use it for nearly a year.
Of course, the traditional method of installing the OS starts with burning the downloaded ISO file to a DVD, which you then pop into your desktop or laptop. That's fine if you have a desktop or laptop, but what about all the netbooks out there? They're notoriously devoid of optical drives.
Fortunately, there are ways around this problem:
1) Buy a USB DVD drive. This is by far the easiest solution, and it'll simplify installing any other software you may have on CDs or DVDs. I've seen external drives selling in the $40-50 range on eBay. Shop around and you may be able to snag one for as little as $20.
2) If you have a USB flash drive with at least 4GB of storage, you can make it bootable using the open-source Live USB Helper utility, then use the free Daemon Tools Lite to "mount" the ISO file to the drive. With that done, you'd boot the netbook with the drive plugged in and select it as your boot device. However, installing Windows from a flash drive can be very time-consuming--and the two aforementioned setup steps aren't exactly novice-friendly.
3) If you have an external hard drive, you can copy the ISO to it and boot from it, just like the with flash drive. Okay, it's a little more involved than that, but this is definitely the easiest method that doesn't involve buying a DVD drive. (It's much faster, too.) Check back tomorrow for a detailed step-by-step.
In the meantime, if you've already installed Windows 7 on your netbook, let me know what method you used--and, of course, how you like the OS!