Vista isn't as bad as a lot of people make it out to be. Compared to XP, it is indeed better, but unlike XP, it is very demanding.
To run Vista, you will need a good computer. Not an ok computer or a decent one. It will need to be pretty good.
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LoginI would recommend you do NOT run on anything less than 1 Gb RAM and your processor should be at least 2.0 Ghz(preferable a dual-core processor). With most newer computers HD space isn't too much of a problem. Vista does take up more space, but if you have a 100+ Gb HD, it shouldn't matter.
If you are already using XP and have a good enough computer, get Vista. There are things in Vista that are very helpful, such as the networking. I work on wireless networks a lot and Vista has been the easiest thing to work with.
Also the updates are very helpful as well, since you can get Windows updates and updates to softare and drivers for your computer as well as some bonuses.
You might get a bit tired of a lot of the messages and alerts, since Vista has a new admin user system. You have to grant permission for certain things to run, kind of like Linux(if you have ever used Linux).
But overall I will give Vista a 8/10.
It is a good operating system and does make using the computer easier(unless you are a novice).