You'd need to get GCFScape and get to the respective game's GCF's. There's no way to uncompress them with Steam itself.
No i mean view them, like trying to use model viewer without steam.
Oh, I see what you mean them. Closest thing would be to get a .mdl converter and get a modelling program.
And out of the sourceSDK?
I guess you could use the MDL Decompiler and open the models in MilkShape.