oooh i thought you meant Iceworld type textures... Well there is no real "ice" texture. Look in your half life thing and there is a kinda wiggly looking glass texture.
**called Generic028c** Put it on your ice and choose To Entity - make it a func_wall. Under Render Mode chose Texture. Under FX Ammount make it something like 150. <- Change that number lower to make it more see through and higher to be more solid. I think that will make it look very ice like depending on how well you do it. Maybe you could make it a little reflective using the the example maps "Reflective water" technique (In example maps section). I hope that all the stuff I just said will help, I tried to be very precise