Can I upgrade my Systembuilder versions of Windows Vista Home Premium and Ultimate to Windows 7? If so, how much will it cost?
If you are talking about OEM, yes you can.
Your OEM licence is tied to a single machine, but if you buy an upgrade, you upgrade that licence to Windows 7.
You set no location in your profile, so I cannot really advise on price, however if you are in the UK or one of the few other countries with pricing anomaly, I would recommend buying a fully packaged product copy as this will allow you to install on any machine and change it to another in the future... especially as it is cheaper than the upgrade copy.