Any advice I would give regarding your system wouldn't be valid without seeing it. Call around for some estimates. I'd bet the last guy to do work on your system left a sticker on it somewhere, but call around anyway. Get at least 3 opinions-estimates, and go from there.
When was the last time your system was drained and refilled? You wouldn't believe how ugly that water can get... Are all of the radiators-fixtures-valves working properly? Have all of this checked while you have the guys there, too.