Building indexes

Greetings!

We are working on a 4 million record db with about 55 fields.  We need 
to build indexes to speed queries, but it seems to take way too long.  
Here are some questions:

1) If a query uses two or three fields is it best to prepare an index 
with those two or three fields, or will the query be just as efficient 
if we build three separate index, one for each field?
2) Is the index building process any slower, per index, if you are 
building more than one index at a time?

Does anyone have any suggestions about building indexes?

Thanks!

- Ron