I just picked up a cheap rm 125 (I know it isn't ideal for trail riding, but it was a great deal) and I'm looking for a place close to Round Rock to get some time on it. I've ridden cruisers for years, but haven't done any real trail riding and would appreciate any recommendations.

You can try Central Texas Off Road (CTOR). Look on the Forums list for info (under the dirt bike/atv clubs section). It is west of Salado, south of Stillhouse Hollow lake. I've been there a few times over the years and it has a real good variety. I think for non members, you can call the land owner and get in for $20.