Running SO Mgr on the server isn't an issue.
Running HQ Server and HQ Client on a box that hosts both databases is a performance disaster.
If the HQ Server is on another box, running HQ client is OK.
BEWARE: According to MS, SBS 2003 is a UNSUPPORTED OS for hosting RMS HQ or Store Ops. When we bought RMS (v1.2) SBS 2003 was a *recommended* OS. I had some transaction weirdness (transaction had the wrong total), called my partner, partner referred the issue to MS. MS replied: RMS database hosted on SBS 2003 not supported. For more assistance, buy a supported OS, stop using SBS 2003 to host RMS, re-create the issue and call us back. We'll be glad to help. Worthless support, IMO.