At the risk of sounding like a stuck record on this one........
About 18 months ago I had an old Compaq that was acting up, it seemed that as it was failing, memory hungry processes were causing it to do hard shut downs. Well, thats another story, but on the back of that I decided to put Linux onto that machine just for a bit of a nerdy challenge. I'm definitely in the 'user' category, my hacking skills in any OS are non-existent. But I had a crack all the same, with Suse Linux 9.3. I bought a retail box, in order to get the manuals, and bought a Linux for dummies book also.
If you like messing with PC's, I treat them a bit like tinkering with an old MG in the garage, a productive waste of time or an alternative to sudoku, you will love Linux.
I've been through a couple of new releases of Linux, each upgrade brings its own new challenges. For me the repetitive bugaboos are WiFi and .wmv file handling. Both are easily sorted once you get the hang of it, but the learning process does take a little time. So now I have a full hand of operating systems at home to compare: XP desktop (kids), IMac OSX (Mrs C) and my own Thinkpad with Suse 10.1. After 18 months of Linux, it is easily my favourite OS. I would recommend trying it. Just do accept that there will be times when you need to scratch you head and go looking for solutions to things that might come easily to XP. Often its not the fault of Linux, but the fact that hardware is not supported to the extent it is in Windows. It can be an enjoyable challenge, and I have not yet been beaten. Not bad for a user, and one in the eye for Bill.
For Suse, I found this website invaluable:
http://www.thejemreport.com/mambo/content/view/254 And if you are trying it for the first time, do spend the small amount of cash on a retail box, as the manuals are very useful for learning the basics. Once you have the basics, there will be no stopping you, and you will be evangelising like the rest of us MS - free outlaws! To answer your original question, yes it is a credible alternative to Windows. You can read and write in word, excel, powerpoint, acrobat formats, manage your MP3 files, watch DVDs, surf anything you can do with Firefox or Opera, network other machines and printers, run a WiFi ADSL router, download movies all the usual stuff - and all for free. The only thing you may miss is access to all those games. Give it a go.