This is a common question, trying to decide the best amount of Physical RAM for your computer running Vista. Even though Microsoft recommend 1GB to run Vista smoothly, that is not really enough unless all you do is browse emails and internet. At the price RAM sells at now, there is really no excuse to say that RAM is too expensive / Vista uses too much. At under $20/gig, you can easily stock up on 2GB and not break the bank.
Windows Vista BasicMinimum = 512MB (0.50GB)
Recommended = 1,024MB (1.00GB)
Gareth's Bloggie recommends = 1,536MB (1.50GB)
Windows Vista Home PremiumMimimum = 1,024MB (1.00GB)
Recommended = 1,024MB (1.00GB)
Gareth's Bloggie recommends = 2,048MB (2.00GB)
Windows Vista BusinessMimimum = 1,024MB (1.00GB)
Recommended = 1,024MB (1.00GB)
Gareth's Bloggie recommends = 1,536MB (1.50GB)
Windows Vista UltimateMimimum = 1,024MB (1.00GB)
Recommended = 1,024MB (1.00GB)
Gareth's Bloggie recommends = 3,072MB (3.00GB)
You may need more than the bloggies recommended, but going with less certainly impacts your computers overall performance.
Cheapest place to buy RAM
www.newegg.com - Newegg have great deals on RAM, starting at $16.99 per 1GB Stick.
www.ebuyer.co.uk - Ebuyer have good deals on RAM, starting at £13.00 per Gig