Microsoft has a good article (KB918483) that explains why it is so important to grant the "Lock Pages in Memory" right to the SQL Server Service Account when you are running 64-bit SQL Server 2005. According to the KB, this only applies to SQL Server 2005 Enterprise Edition. I previously talked about this over a year ago when I first ran into the issue.
They also have another article (KB889654) that explains how to size and configure your page file on 64-bit Windows Server 2003.
Speaking of RAM and SQL Server 2005, obviously, more is better. Having more physical RAM increases the chances that you will find what you need in RAM (so you get a logical read instead of a physical read), which will reduce the pressure on your IO subsystem and have a huge effect on performance. Many quad socket servers (such as the Dell PowerEdge 6800) have 16 slots for RAM. Until recently, the sweet spot (financially) for a system like this was 32GB (since 4GB sticks of RAM were so outrageously expensive). Now, if you price out a new 6800 on Dell’s web site, the price delta between a new system with 32GB and 64GB of RAM is only about $6000, which is a huge improvement!