If you are comfortable using XP you should have few problems with normal
day to day use of Ubuntu. The biggest differences you will find are
* Security is taken far more seriously in Linux than in Windows. Many
Windows users don't like this as it 'gets in the way' but it makes the
system far less likely to be compromised (do not believe the myths that
Linux is immune to malware, it isn't, no computer system is. It's just
that Windows is *so* much easier to exploit that the script kiddies
don't bother with Linux)
* Support in Linux is provided in an *entirely* different way to
Windows with almost total reliance on community support rather than
commercial and an emphasis on teaching you how to learn and understand
the system so that you can help to support yourself, rather than
step-by-step instructions-for-idiots that teach you next to nothing
* The way software is installed and managed is radically different, but
much easier once you get used to it
* There is quite a bit of hardware that will not work in Linux, but the
situation *is* getting slowly better
* There is more use of the command line to perform tasks. Indeed, many
power users *only* use the command line and don't even install a
graphical desktop
* If you're a gamer, you'll find few of the games that you play are
available for Linux - again, this situation is slowly improving
There are Linux versions of most of the programs you are familiar with
in Windows and for those which don't have a Linux version, there's the
Wine project, which allows (some) Windows programs to be run in Linux.
All in all, having switched from XP to Ubuntu myself just over five
years ago, I'd say you'd have few really serious problems making the
transition. However, I would strongly suggest one of the 'try before
you buy' options such as dual booting, Wubi or simply running it for a
bit off the live CD to make sure your hardware works and to get the feel
for it before you totally wipe out Windows (noting that the live CD is
slower than a proper install as is, I believe, Wubi)