My own opinion on probably the best Linux distribution to use is Mandrakes latest one (for a new user the best I think). They have changed the name to Mandriva. You can probably pick it up off the front of some of the recent pc magazines or else if you have BB just download it. Theres nothing to stop you doing a dualboot system to see which you prefer (windows and linux on one machine).
www.mandrake.com
Its an easier install than windows, comes setup by default for a basic user and pretty much just works.
Frankly I don't think at this point that most Linux distrubtions will suit any non-techie type except for those who have a specific set of requirements (email, web-browsing, Multimedia, Office type apps).
It is ideal for users who will use it for basic stuff and it is "relatively" invulnerable to the usual virus/security issues.
Openoffice is very compatible with office documents and spreadsheets (apart from very specific coding in the excel sheet which does something out of the ordinary). I use it more often than I use MS-Office based stuff and it does the job fine. I think there is a version of openoffice for the mac also.
Linux runs 2 alternative desktop solutions (ok theres more than that but the 2 main ones) which are KDE and Gnome. KDE is more of a "standard" windows experience while Gnome is more mac like (in my own opinion).
Mandrake Linux runs KDE as its default desktop.
Its hard to know what would be most suitable for you but if you don't want to run windows its a good starting point. I think its unlikely that you will buy a laptop without an Operating system installed and most likely this will be windows (you pay for the license usually in the cost of the machine). The mac laptops are usually much more expensive in my limited experience with them. Usually pretty but underpowered compared to their x86 counterparts.
Regarding browsers on windows. Firefox is the current premier browser out there. Microsoft will be launching IE7 sometime later this year and have borrowed heavily from what Firefox already has. Also IE7 will only run on a windows XP machine. So if you've not got XP then you are as well off getting used to using firefox anyway. Firefox also runs on linux.