I was interested in this one, as I've recently got an Acer Laptop, on
which I've installed Ubuntu 8.04.

Do you get the choice of the two options, every time you switch on? If
so I'm puzzled, as you would only want a recovery option in special
circumstances.

Ideally you should create a Vista bootable installation disk and also
backup any important files and data before installing Ubuntu.

You'll probably need to reduce the size of the last Windows partition,
to create some free space for Ubuntu, say 30 to 50 GB. Use the live
version of Ubuntu for this.

Ubuntu should then install OK, and produce a dual boot system.