New user questions

I'm thinking of buying a 12" Powerbook, and probablly i will.the main questions are:
* Do i need to buy more memory (upgrade to 1GB) or the 512MB do the job?
* Regarding batteries: sould i buy an extra? hen connected to the power outlet do i have to take the battery off?
* What are the must-have softwares?

thank a lot,
best wishes from brazil

I forgot to ask. apart from the startup password, is there a way to protect by password specific files/folders?

What programs are you thinking of running?

the basics, for internet, e-mails, video playback, recording and ripping dvds,
specific, images editing like photoshop.....
i've heard that some programs that i'll need for college (i don't know the name) are windows-only. is there a way to make them work on a mac?