Laptop help

[jumpy]

My aunt has an older laptop (1gb ram not more than 1.7ghz cpu) with vista home basic (32bit) and recently had some issues with a virus or two.
She has a new copy of norton internet security (bleargh) 2010.

This was duly installed by me and cleaned the computer, but it shafted her internet connection, so that even with NIS un-installed her internet was broken. Proxy server issues.

Any way, after removing NIS, I tried the following 4 free av software:

Avast (what I'm currently using)
AVG
Avira
Comodo

Avast had some error about split profile or some such, and had to be removed in safe mode with a special uninstaller.
AVG failed to install correctly.
Avira was a whole bunch of files in a .zip with no installer or setup.exe
Comodo installed just fine, but did nothing, refused to run and now cannot be uninstalled (looked online and you can remove it using the cmd prompt, but this looks like loads of grief)

Currently she has no working AV and I cannot for the life of me think how to fix this.

Her user account is Admin, so I wouldn't have thought there's any rights issues, though I could be wrong.
Also the windows task manager is missing - ctrl-alt-del brings up a menu to switch user/lock etc, but when you select task manager from this list, FA happens.
I'm used to dealing with XP and as far as I'm aware, Vista was a pos from the start.

Her laptop was second hand so there is no install or windows disk, but there is a partition which I'm assuming to contain the backup/install info. I could be wrong.

I'm considering attempting a system restore point in the hope that it will leave me somewhere after NIS but before Avast.

I'm pointing the finger of blame firmly in the direction of vista and its babysitting 'are you sure you want to do that' in triplicate warning system any time you want to do anything to modify a program. The OS is up to date.

If it was mine I'd look for a copy of XP home or W7 and use that after scrubbing the whole damn thing clean.
The machine itself is ok, but the os doesn't seem to be co-operating.

I'm relatively tech savvy, having built and maintained my own desktops for over ten years, but this laptop is causing me to rage lol. Any of you guys who could shed a little light on the sitch, would be a real boon.

Gotta try and get my head round this by wednesday, as I promised to go back round and fix it after consulting the internet (you lot )