[svandamme]

"uninstalling" virusses and trojan's can be done without a reinstall
but frankly , it's very difficult and time consuming

you need to scan offline, eg, without booting from the disk
and since hardly any good uptodate virus scanners exist in dos (to scan with ntfs4dos)

your best bet is to put the disk in another machine that has a bullet proof scanner installed and running real time...
and if you don't know what you are doing, you could infect that box too

so unless you know what to do without guidance, i'd say a format/reinstall is your best bet