First a white paper with all the info needed to move the various data stores to another drive, an absolute necessity in my book.  It’s best to plan on doing these changes early so you don’t run into issues later with low or no disk space.

http://www.microsoft.com/technet/prodtechnol/sbs/2003/maintain/movedata.mspx

Second, info on how to limit the amount of memory used by the SBS Monitoring process – use with caution, but I’ve yet to see any bad results, it just limits the process from using up way too much memory:

C:\>osql -E -S SERVERNAME\SBSMONITORING
1> sp_configure ‘show advanced options’,1
2> reconfigure with override
3> go
Configuration option ‘show advanced options’ changed from 0 to 1. Run the
RECONFIGURE statement to install.
1> sp_configure ‘max server memory’,256
2> reconfigure with override
3> go
DBCC execution completed. If DBCC printed error messages, contact your system
administrator.
Configuration option ‘max server memory (MB)’ changed from 2147483647 to 256.
Run the RECONFIGURE statement to install.
1> exit
C:\>

Note: Replace SERVERNAME  and the 256 setting with values to match your system – I usually keep it at 256.  I find without this setting, an SBS system left on it’s own will use a huge amount of RAM associated with this process

Third, this is really just a subset of the first white paper, but focuses only on moving Exchange databases to another location: http://support.microsoft.com/kb/821915

Finally, a couple of links helpful when you’re moving from a non-SBS domain to an SBS server:

How to install Small Business Server 2003 in an existing Active Directory domain – KB 884453

and a more general:

How to replace single domain controller in domain with a single domain controller? – KB 555549