There's only 1 useful site that you can use to "cheat" the 205 into turn by turn:
The major differences between BRT and the other sites that are useful to the 205 are:
1) BRT inserts a course point automatically at the turns
2) You can edit those course points on BRT's cue sheet page
I then download the file as a .tcx to the Garmin Edge and from the device's menu I select Training --> Courses
I'll pick my course, then select Do Course.
On the 205's Course screen, one of the fields is a box called "Dist to Crs". This box will show the distance to the next turn, a direction indicator that tells you the direction of the next turn, and the name of the course point. The name of the course point is only 10 characters, but that should give you enough of an idea of what to look for. At the turn, it will beep at you and flash the course point info across the screen.
If you go off course, it will tell you, and also tell you how far (as the crow flies) back to the route. The map helps tell you which direction you're off, but usually it'll tell you darn fast that you missed the turn.
BRT also gives you the option to add Course Point Warnings, which is essentially just another course point that appears 200 ft (or whatever you specify) right before the turn. I tend not to use this, but the option is there.
This is kind of nice trick if you really can't afford a true Navigation unit. But shop around. The eTrex will log your progress and give you the turn-by-turn, plus probably some true elevation data (Garmin 205 doesn't have the altimeter). If you're patient with computers, you can get the Edge 705 off of ebay for under $400, buy a MicroSD card for less than $15, and either pirate the mapsets, or get them off of GPSFiles.com or Cloudmade.com - I'd assume that the 605 is even cheaper. Seems to be quite a price bump to get them with the Mapsets included.