Help me technically minded people! You're my only hope...

So, shiny new computer is finally here, and plugged in, and... running Windows Vista.

Yeuwch!

Quite apart from the fact it's trying way too hard to be a Mac (and failing miserably) it appears to come with all kinds of intrusive security stuff. (For example, I deliberately ordered it without any kind of bloated Norton-type security software but there still seems to be a bunch of McCaffee stuff running in the security centre.) Generally I prefer to run trusted, FREE software - my netbook currently has Avast as an anti virus and Comodo as a firewall with a few anti-spyware things as back up. So:

a. Any reasons why I shouldn't install Avast, Comodo etc on the new machine instead of what's already on there as part of Vista? (ie there are better free ones, the ones that come with Vista are okay, etc)

b. What of what's on here can and should I get rid of, and how do I go about doing that? Deactivate things? Uninstall completely? I'm always paranoid about deleting something vital, but I know two firewalls can end up fighting...

c. Does Vista come with partitioning software, or if not what should I use? Have one big disk and want to partition it, not least because an upgrade to Windows 7 was part of the package, but as far as I'm aware you have to do a fresh install when that turns up, so that way I could just format the partition rather than the whole disk. (I think this makes sense. Does this make sense?)

I am a relatively smart non-techie (with a techie housemate who refuses to touch Vista with a bargepole, and I can see why, but I'm willing to give it a go for now) so please phrase any replies accordingly!