changing rear cassette to less cogs?

The spacing between each cog is different, which means that your indexing on the your shifters won't match up. A 7-spd race wheel must be quite a few years old, and although it can still be in great shape, keep in mind that things to wear and if it has been in storage, seals etc. may have dry rotten. The hub spacing may also be different on the 7spd wheel (126mm) versus the 9 and 10 speed spacing of 130mm.

The only way to even make the 7spd work (as long as it's 130mm spacing) would be to use the non-indexed shifting (which you can do on Shimano, but not on Campagnolo, and I don't think you can on SRAM). Otherwise, your index points on your shifters won't correspond to the spacing of the cassette.

In my opinion, you my be better off looking at a used wheel that can accommodate your 9-spd cassettes.

The wheel is most likely a freewheel, which means buying a new cassette won't work, either.

If by chance it has a cassette hub, putting on a 9-speed cassette is quite easy. However, that they still have the 7-speed setup attached leads me to believe that it's a freewheel and not a cassette.

You can use your 9-speed shifters in friction mode. It's quite easy once you get the hang of it.

It's a solid disk from another tri person so i higly doubt its a freewheel.  I have 105 shifters, will this be ok? The price is so good changing out the old bearings and getting a new tublar will be well worth it.

If you're planning on using shifter/brake levers (instead of bar-end shifters), it won't work. There is no way to get friction shifting with STI shifters. Find out if it's a cassette or freewheel, it's a simple question.

They made LOTS of disk wheels with freewheels. Depending on the manufacturer, you may be able to send it to them and have the hub replaced, but it'll be around $100 or so for that.

Yeah, I know that errthang 8/9/10 is compatible, and stuff changed from 7- to 8-speed.

One can even find a 9-speed freewheel, but it takes some searching. And by some, I mean a lot.

All this is a mute point though if the hub is 126mm spacing, which is quite likely on a 7 speed. The 8-9-10 speed spacing is 130mm.