To echo what the others have said you'll find you can do much of what
you did on Windows but there will be some things that will need a
different approach. General stuff like e-mail / web surfing etc is
just the same and working with photo's is as easy / easier too. Things
like iTunes and working an iPod are troublesome but not impossible as
long as you realize that it won't look or work in the same way.

Overall many of us find that the plusses far outweigh the minuses but
you won't know personally until you give it a go. The Live CD will
give you an idea, and Wubi will allow a sort of dual-boot with a
slightly less able Ubuntu installation but more workable than the Live
CD.

Once you decide to take the plunge then a full install will open up
the full 'Ubuntu Experience' and where you go from there is up to you.
It's perfectly possible to have WinXP loaded using Virtual Box and get
into iTunes that way if needed - and WinXP works better that way than
natively though it won't run high power games that way.

If you do decide to switch there's plenty of help around to get you up
and running plus deal with problems as they arrive. Some things will
not work - Lexmark printers being notable in that respect but all
makes of peripherals will have some models of printer / camera etc
that will not work under Ubuntu no matter what you do.