I have Exchange Server 2003 running on Windows Server 2003 SP2 but I don't have any of the service packs on Exchange yet. Since there is Service Pack 1 and Service Pack 2, can I install Service Pack 2? Or do I have to install SP1 first? Thanks.

You can install SP2 directly. http://download.microsoft.com/download/f/b/5/fb5c54af-fe5c-48e9-be97-f9e8207325ab/ex_2003_sp2_relnotes.htm Anil

Do I have to wait until the users are not using it? For instance, should this be done at night? As a rule, I usually do all of my updates at night or on the weekends however, I am running out of time.

i will recommand to plan it in week end, as while applying SP it will take all the exchange services offline (this will result in users lossing connectivity with exchange server). and if there is any unplanned downtime you can continue in weekend as users wont get affected. and before applying SP please backup exchange server.

Okay, thank you!!