set up

You shouldn't have any problem tuning down half a step. If you have a floating bridge, it might be a problem, but you'll be able to tell after you've tuned down.

You should be good to go only a half step. Intonation should still be good. As Musenfreund said, if you have a floating bridge that most likely will need to be adjusted. If it is a Floyd type bridge (double locking) you will need to be sure to keep the bridge level with the guitar body. This will usually mean loosening the claw in the rear cavity. If it is a vintage style Fender type trem you may still be ok. If it raises too far from the body, again the same adjustment from the claw is needed. Some Fender type trems can be stiffer than Floyd type trems so you may still be ok. If you have a fixed bridge then you should have no troubles.

My guitar has a Tune O matic style bridge. So I do need to have the neck reajusted or anything?

Ignore my last post I didnt read everyones posts. Thanks for the help.

I have another qestion about tunning down. What about string gauge? Should I buy a set for down tuning?

If you're using fairly normal strings, you should be able to tune down without any problems.

Might be a good idea to do a search (on this helpful forum, for example) of info about set ups.

Just to tune down a half step, I don't think it's likely to be an issue. (I sometimes tune down a half step to play along with Guns and Roses, then tune back up to play along with somebody else, in the same practice session. No problems.)

But, since you're thinking about set up, you might as well learn to check it. If anything changes with your guitar, check the straightness of the neck, string height at various points, the position of the bridge, how to raise and lower saddles (or bridge) and change intonation...

I don't think it's necessary for what you're talking about, but it's easy, fun, and good to be able to do on your own.

Best,
Ande

In what situation would I have to change something on my guitar. If im changing tuning to any alternate tuning would I have to do anthing to my guitar? or can I simply just tune and play.

With a tune-o-matic bridge you should be fine for alternate tunings. With a floating bridge though, the intonation can change dramatically with alternate tunings and need to be adjusted.

thanks for the help. :D