Dual-boot or run VirtualBox, as recommended, to get a taster of the system before going completely over. I started with Ubuntu in WUBI, but that just annoyed me, so started dual-booting, eventually made me go over completely, but that is a personal choice. Was running XP in Vbox for awhile, but lost the .vdi when I was playing with partitions, and haven't bothered reinstalling it.
If you are trying Ubuntu, I would recommend bookmarking
Ubuntu Forums, there is a wealth of useful information there for the newcomer, and it's where I've found 95% of my fixes for any issues I've had with Ubuntu(the other 5% was Google, lol).
Bought my printer after fully migrating to Ubuntu, before I made the purchase, started at linuxprinting.org as I wanted a printer that worked with little or not effort in Linux, decided on HP due to the fact that there are already drivers included with Ubuntu, found the printer that was within my budget and have never looked back.
Running Ubuntu, or your distro of choice, in a dual-boot or Vbox setup will let you test that all your hardware is compatible, or if not, you can see what fixes are required to get it working, if any. Then you must decide if it's worth it. Had no issues with HP Printers(as already mentioned), Nvidia, Razer (mouse), Cell C (& Vodacom) USB dongles and Microsoft Keyboard and Headsets (

). Had to hack around a bit to get full 5.1 out of a Soundblaster Audigy 2, but it's working nicely now!. Apparently there is better support for ATI now, but I can't testify to that fact as I've never installed Linux on a system with an ATI GPU. Not sure how good support is for onboard graphics and sound either, same reason as mentioned for ATI.
That's been my experience so far, and as others have mentioned, you will need to change your mindset a bit as well, as Linux is indeed not Windows, it is a whole other OS, not just a piece of s/w.
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