Is there a way to speed up an ALTER statement in SQL Server
You're using Enterprise edition, so you should be able to use online indexing. Add the WITH ONLINE = ON option to your index DDL statement. The operation will still take just as long (possibly longer), but SQL Server will do some magic to keep the table accessible throughout. Here's some documentation with assorted restrictions, but they mostly only come into play if you've got LOB columns in the table:

http://msdn.microsoft.com/en-us/library/ms190981.aspx

This won't help you with altering the column data type, of course. If it's constantly being inserted, but not necessarily updated or read (and you can live with such operations being unavailable during the transition), you can rename the original table, create a new one with the desired structure and permissions, move all the data over, then recreate the indexes on the new table. This may be slightly more complicated if you have an identity column and want to preserve values, but it's still doable.