Well, I wanted to know so I could do some testing since I really don't like giving out untested code. I know a way is possible, but I was hoping to have all information in front of me before testing. I really don't want to ask again though so I'm going to pass. I have an alternative for you though that is a lot simpler and I've already tested it. Create another field and ask the users to enter their steamcommunity IDs (i.e. bogbouncer).
Then use that field to provide the link for your SteamID#. Basically, you'll still display only the SteamID#, but it will then use the other field to generate your link.
Code:
<td class="$bgclass" nowrap="nowrap" align="center"><if condition="($user[field42] == '')">$user[field9]<else /><a href="http://steamcommunity.com/id/$user[field42]">$user[field9]</a></if></td>
field9 = to the field number of your SteamID#. (i.e. STEAM_0:1:17768031)
field42 = to the field number of your Steam Profile ID. (i.e. bogbouncer)
Much easier. Enjoy and good luck with your roster.