does anyone know a good way to weather a tank or know a site that could tell me

Go to the Features section of this site, then go to the Armor/AFV section and you'll find numerous articles on various weathering and detailing techniques. HTH

LittleNick, there are lots of ways to weather a tank. Most modelers follow tried and true techniques in a set order to achieve a weathered tank.
A common set of steps that are followed are as follows:
Build, apply overall paint color (camo if desired too), apply a coat of clear gloss, set decals, apply another clear gloss over set decals, apply a wash, apply a clear flat coat, dry-brush, apply pastels, apply final protective clear flat coat. Take pictures and show everyone.
As you can see there are lots of steps in order to achieve a well balanced weathering effect to your models. If you would like each step broken down in easy terms, let us know and we'll be happy to oblige.

Kencelot's right; the process is pretty involved but the techniques themselves are generally not difficult to master. But let me add that half the battle is PLANNING! This means thinking about the effect you want as you build the subject. Some effects, like heavy mud, might be better applied (or partially so) in the subassembly stage to make things easier to work around. Also, the environment determines the weathering. Obviously a tank at El Alamein won't have mud; it's desert sand there. But Tunisia sure might, depending on the time of year. See what I mean? HTH :-)
Greg

Howdy LittleNick,

Well, there ya go! In short order you've had 3 great answer's there Nick! Phantom was kind enuf to point out the almost bottomless source of info/answers available on this site.
Our valued member Kenc' has given you the reader's digest version in a sentence (good isn't he?)
And, finally, our Greg has empowered you with one of the most useful tools in modeling
'PLANNING'!
Armed with these alone, you're wayyyyyyy ahead of the majority of us when we started modeling.

Tread.

...further tho' Nick, ask and ye shall receive.

Follow what these guys say It's easy to get the hang of :-)

Matt