Does the type of lenses you have determine photo quality?

I'm thinking about buying a Nikon D5000, but the lenses are so expensive.

Lenses have a LOT to do with image quality. Decent lenses are expensive for a reason.

Lens quality is the only thing you can see makes a difference, but there are many older lenses that be as good as the best modern ones, the laws of optics haven't changed, what was a good lens decades ago will still perform as well if not better than some modern offerings.

If you want high quality lenses at a cheap price go with the Pentax system, over 200 lenses with the K mount lens available and that's just those made by Pentax.

If you buy a Pentax A series (auto aperture) 50mm f1.8 lens (average cost less than £100.00 usually around the £60.00 mark) the only thing you'll be missing is auto focus.

Image stabilisation is built into the camera so even these older lenses are image stabilised. No extra cost for that.

Plus you'll get All the functions, some only available on a Pentax. Great build quality and the cheapest system to buy into by far.

One of the best systems for using these older lenses is the micro 4/3 system (Panasonic G1 or G2, Olympus EP-1 or EPL-1). These have such a short lens mount to sensor distance (20mm) that you can use lenses designed for TV cameras, lenses for 35mm hollywood type cine cameras and lenses for the old leica cameras, with adaptors. These are some of the finest lenses available, you can't use them with normal DSLR, but with the micro 4/3 system you can.

Lenses can be expensive for a couple reasons, one of which is quality. Forgive the Canon examples, it is the brand I know best.

Here is an example of quality, although the size of the lens is also a factor here:
http://www.onecall.com/product/Canon/EF-70-300mm-f4-5-6-IS-USM/Lens/_/R-29551
and the better:
http://www.onecall.com/product/Canon/EF-70-300mm-f-4-5-6L-IS-USM/Lens/_/R-106534

The size and number of lens elements (Particularly the objective) also effects price like these two:
http://www.onecall.com/product/Canon/EF-70-200mm-f-2-8L-IS-II-USM/Lens/_/R-102512
http://www.onecall.com/product/Canon/EF-S-18-200mm-f-3-5-5-6-IS/Lens/_/R-93039

Also, faster lenses tend to have better glass and an iris with more but thinner blades to create a wider maximum opening. Most of the price is in the glass, which generally has fewer elements, but each element has compound grinds. Take these three 50mm prime lenses:
http://www.onecall.com/product/Canon/EF-50mm-f1-8-II/lens/_/R-4766 plastic and slow.
http://www.onecall.com/product/Canon/EF-50mm-f1-4-USM/lens/_/R-4765 getting better.
http://www.onecall.com/product/Canon/EF-50mm-f-1-2L-USM/lens/_/R-33749 fri@@in awesome

Image stabilization, weatherproofing, stationary front rings (don't turn when you focus or zoom, helpful when filters or macro flashes are used), all contribute to a lens expense.

Lens quality is a huge part of it. I'm not convinced that sticking a $1200 lens on a D60 is going to make a big improvement, but I do know that sticking a kit lens on a D3 is going to ruin the images.

I have to agree with Chris - the Pentax K-x would be a great choice. So when the time comes, give Chris the 10 points for "Best Answer".

Lens quality is on up there in importance. Lighting will make or break an image long before a lens will though.

While some lenses are better than others, I wouldn't get too caught up in that right now. Realistically, there are no terrible lenses on the market. Even the kit lens when stopped down a bit is decent, and it's considered bottom of the barrel. I've shot most of my 365 with it and the results are just fine. I'm not making any huge prints with the kit lens, but as a general lens it's ok.

I would end all that saying that yes, the more expensive lenses are in fact worth the money. Unless you're doing professional work then don't sweat it. Get what you can afford and don't look back.

Yes.