Can't install v3 or remove v2.5

I've had v2.5 installed and used for some time. Today having not using for a while, running 2.5 asked me to upgrade to v3. I dowloaded install and ran it but it freezes at the 'validating install' part of wizard. Tried again (after hafing to end task and end msiexe process) still freezes. Via Control panel I've tried to remove 2.5 (and repair) also freezes. So basically I'm stuck. Any suggestions? Are there any shortcuts to removing this application so I can try a clean v3 install... short of some very long-winded editing of registry? I'm using XP Pro SP2.