Hi Ian,
Most modern drives are excellent - just stick to the well known makes and you will be OK.
Samsung, Seagate, Western Digital, Hitachi all make good 2.5 inch SATA drives - all you will have to decide is the spin speed 4200, 5300 or 7200 RPM. Faster speeds are quicker transferring data but are more expensive, draw more battery power and are noisier - lower speeds are quieter, cheaper, slower and use less power.
The only thing you need to check is the height of the drive - make sure it is a slimline 9.5mm. Some large capacity drives use three platters instead of two and can be too thich at 12.5mm.
You say 'windows 7 upgrade' do you mean you are going to load Vista onto the new drive and the run an upgrade or do you mean you are upgrading with a clean install of Win 7 on the new disc? If you are actually going to upgrade it may be best to take a mirror of the old drive complete with your software, drivers, updates and settings using something like Acronis True Image and put back the mirror on the new drive.
If you are doing a clean install you will lose all the preinstalled Sony software and you cannot recover this.
Swapping the drive is very straight forward:
