SQL / ASP application speed problems

I have a SQL database that is about 300 mgs, running on it's own server, which has been souped up with a decent processor and several gigs of memory.  I have 6-12 people access it through their intranet during the day.  The database contains 80,000 records.  When I'm logged into the server I zoom along fairly quickly , except when I run large reports.  However everyone else's speed is sloooooooow.  

I'm not a network person and I'm running out of excuses why their access could be so slow.  I'm looking for some general knowledge/suggestions.  

They don't have individual user accounts in the SQL database, they all use the Guest account.  Is that slowing them down (like too many people accessing the same internet connection in a home)?  
Many of hte tables are large (in terms of columns), but it's unavoidable, could that be slowing them down?  And if so, why doesn't it slow me down when I'm running the same pages directly on the server?
What else is there in the nexus of ASP, SQL and a server (NT) that could determine how fast people are quering and viewing data?