If you are thinking too much about the hardware requirements to deploy Vista (especially RAM and GPU), the Microsoft Vista Hardware Guidance posted very recently should help.

If you want Glassy look of Vista, must go for the vendors listed from the same article, which supports Windows Vista Display Driver Model (formerly known as LDDM), else Windows XP-comparable desktop graphics experience will be provided. Currently Intel, ATI and NVidea has LDDM supported GPUs.