You mean they're supposed to move??????
As for the hammer, yes, I have a small rawhide mallet, which I used to use primarily for removing rotors from my french horn (before I reformed) Using a mallet on slides is pretty dicey, if you use a curved block of wood, and a lot of care you may be able to tap it out, but I'd try the warm bath.
I'm not so sure about the boiling water method. If it works (and I'm sure it has for whoeve suggested it, I'd think it's because of the water, not the boiling. If you think about the physical properties of the metal (expands while hot, contracts while cold) then remeber that you have tubing that expands in both diections (i.e. the slide doesn't just expand, the thickenss of the slide's tubing expands, as does the inner tube) so it would make the fit tighter, not looser, so I'd suggest maybe a warm bath (with candles, and a glass of Pinot Noir, skip the bath salts) then if that doesn loosten maube some cold water....(I'd hesitate to recommend ice for fear of popping a weld.)
But those are all just the ramblings of novice, if it's that tough a trip to the shop then lots of slide grease therafter would probably be the best recommendation.