Using explorer, check the contents of both DVDs. There should be folders such as: boot, efi and sources which is very large.

The normal sequence when booting from the DVD is loading files, select language and keyboard and then bottom left is repair, which you should be able to choose.

I don't know much about the way the PC manufacturers set up their recovery options. Sometimes it's a partition, sometimes the user creates DVDs, sometimes full DVDs are supplied. The Acer site will probably give you the information you want.

Note: I should have said that a Vista repair is not the same as an XP repair. Presumably all the personal data is backed up.