Bicycle Mechanics - Single-speed from a 7spd hub

I'm looking to convert my 7spd roadie commuter into a SS but I'm not quite sure about the best way to do it. I've checked out stuff like Gusset's 1-er SS conversion kit but that seems to only work on 8/9 speed hubs. There's also the other option of stacking cassette spacers but I would have no idea which ones to get and where to get them.
I also heard that you can stack BB spacers but I'm not exactly clear on how the lockring would fit in this case.

Please help, thanx

If your 7-speed hub is a freewheel, you are in luck. The conversion couldn't be simpler.

1. Remove 7sp freewheel.
2. Remove rear der and shifter.
3. Screw on singlespeed freewheel of your choice.
4. Shorten chain to fit.

Some notes. I like Shimano ss freewheels; they seem quieter. Check the width of the cog. Some BMX freewheels require 1/8" chain. Shimano uses standard 3/32", ie, any 5,6,7,8,9 sp chain.

Now if you are talking conversion to fixed gear that's a little different.

I'm gonna assume you have a 7-speed freehub. I did this the other day, and it may not be exactly the same on every shimano casette...If yer looking for spacers, get an old shimano cassette, and look at the back of it. There should be the tops of three little bolts. These pass through all the cogs and hold them together apart from the first two (usually). To open these you'll need to get a 4mm socket and screw them out. The whole thing will come apart and turn into cogs and plastic spacers, both of which sit neatly onto yer frehub body. If you can find enough of these spacersthen all you need will be a bunch of them, the sprocket of your choice and the lock ring. Position the sprocket so that the chainline is straightand lock it all up. Chain tension is important, so hopefully you have horizontalish dropouts (ie not verticals) so that you can adjust the tension slightly when you have chain length correct. If you have vertical drops you may find the chain coming off, if so check that the chainline is as straight as you can get it, and chain tension is right. If you want a better guarantee of it staying on, you could position two larger sprockets on either side of the one you're using, but that doesn't guarantee it won't jump off on the front. Hopefully you have semi-horizontals. There's also half-links you can get to adjust chain-length by, you guessed it, half a link, but I don't know how common they are. I've never seen one yet... welcome to single-speed!

have heard of people using PVC pipe as a spacer...

Surly makes a single speed adapter so you can still keep a cassette intact for later. It is basically a group of spacers and one unramped cog that slides on the freehub.

Jenson also sells a set of spacers
http://www.jensonusa.com/store/product.aspx?i=CS701Z00

You have a few options now :)