when to use what lens.. ?

I've been using my dads Nikon D70 and I got a polarized lens for it and a hood, but my question is when is a good time to use either or, and should I ever be using both at the same time? I've been shooting a friend BMXing lately and we shot all day yesterdya and it was sunny in the morning so I thought I'd experiment and use both the polarized lens and the hood, but when I put the pics on the comp they look... I dunno not as crisp and colorful as I was hoping for. They almost seem a little grainy but I think that may be cause of the polarized lens? Later in the day the clouds rolled in and I took both off, the pictures seemed cleaner but with the grey sky the pics still weren't what I was going for. So when should I use the hood and when should I use the polarized lens? Also I've been saving for a Fish eye lens.. is it worth the money and does anyone know a cheap place I can get one? Are there any lenses that you can use on a cloudy day to make the image.. i dunno... more colorful?

here's an example of a pic... (this is w/o both on the grey day)

oops.. lets try that again...

What were your camera setting?
Also cheap filters create cheap pictures.

The hood helps protect the shot from flare and should be used anytime you're shooting in direct sunlight or other strong lighting. This is really independent of whether or not you're using a polarizer, which cuts down on glare or reflections. Note that a polarizer really only works well when your shot is sidelit (ie sun is at a right angle to what you're shooting.) Polarizers cut down the light entering the lens so you need to open up the lens or cut the shutter speed to account for that. If you're just trying to get more saturated color from the sky you might want to try a graduated ND filter or bracket your exposures and combine in photoshop (that's a bit hard to do shooting a moving object however.) If you shoot in RAW you can do your own bracketing with a single shot also. Here is a great tutorial on how to do that:

http://www.luminous-landscape.com/tutorials/blended_exposures.shtml

Bess there's nothing you can really do on a grey day except *maybe* try using a flash. Or just play with it in photoshop and see if you can come up with something interesting. But filters just won't make the sky blue or bring out the colors when it's overcast.

I just picked up the Sigma 15mm fisheye and it's a nice lens. It's not cheap, but it's cheaper than the Canon and maybe you can find one used. It would be a great lens for shooting skateboarding and maybe BMX too.