I run C6 Pro on Vista Ultimate 32 Bit, but I am not sure about C5.  You should know that if you buy a PC from some vendors with Vista,  a lot of them have downgrade rights, meaning if you get Vista and it doesn't work out for you, you can get XP for free and downgrade to it.  I normally never recommend using a name brand machine, custom builds are so much better, but if you are concerned about Vista, this may be an option you should speak with whomever you are planning on getting the new PC from about./