You can make your .Mac address anything. I chose something that was completely irrelevant for my account name.
The only way to get .Mac is to actually buy it, (the $100) find someone who is a memeber and will support you by an e-mail only account, that is $10 a year, or you can try the free trial that lasts 60 days, but once that's done, the only functional part of .Mac is the iChat name in the trial.
If you can afford .Mac (which it sounds like you can't) then don't buy it. I tell people to only get .Mac if they have the money and if they actually will use all of the features.
I would use Gmail. I've heard it's rather good. I wouldn't get anything from Yahoo! or AOL because I have tried and heard from some people that you get too much spam from Yahoo! and AOL.
I think all of these are considered POP3 accounts. In laymen's terms, these will all work with any mail application, whether it's Outlook, Navigator, Mail, Entourage, etc.
Also, switching to a Mac has never been easier! I hate to sound preachy, but here we go. Compatibility issues are never a problem as I have seemlessly shared all sorts of files easily with Windows people. I live, work, and talk to people who all have Macs except for three people and I haven't had any problems.
Also, don't buy the extended warranty or AppleCare. People tell you to get it, but a 1 year warranty is good for me and I've only had to replace one of many Apple products in my lifetime and I found out later on that I didn't have to replace it.
Welcome!