Greg is correct. Steam can easily be moved. However, if you have games currently installed, you may require a few extra steps.
You can move Steam to the HD.
If its already installed, what I would do is this:
1) Make a new folder on your HD called Steam.
2) From your current steam installation, copy the steamapps folder, and all of its contents to the new Steam folder you just created. (These are your games as Im sure you are aware)
3) Next, copy the Steam.exe in the current installation folder, and place it in the new Steam folder you just created as well.
-- So you need just the Steam.exe and the entire steamapps folder. Steam will update the rest --
Now, you can un-install Steam, then run the Steam.exe in your new location and it will update & re-install itself.
May take a few minutes.
Hopefully you havent installed any games just yet.
If so, you may consider un-installing them before you un-install Steam & after you move everything to the new drive.
If you do not, you may end up with broken shortcuts, such as in the Windows 7 game Explorer.
Also, if you have any games that have SecureROM, moving the location might prompt for activation again, even though its technically already activated.
This may take a little while, but you will not need to download your games again. So it shouldnt take too long.
Remember, un-installing the game will delete it from Steam. So be sure youve moved your game folder to the new drive 1st.