There appears to be numerous errors on my copy of Windows Vista Home Premium over the months, especially in the registry where it caused installation errors for iTunes. I don't have recovery discs to repair Windows or reinstall from. If I were to buy a copy from the stores to patch up the missing parts or repair from, which one will I need? Upgrade or Full? Also, I have MS Office 2007 Pro on it. Will I be able to reinstall it once I fix Windows? It is licensed for ONE PC only. Will it count as a second PC if I reinstalled?