I've had a similar problem, not with SQL running slow but with SEP and performance issues on Windows 2008. Questions:
Was your DBA accessing the windows server via RDP?
When you installed SEP did you also install the Network Threat protection (NTP)portion of the client?
If you did install the NTP part of the client do you have a firewall policy enabled?
On my Windows 2008 std x64 system I found that having the NTP installed caused the RDP session to be
incredibly slow. Uninstalling that portion and leaving only the Antivirus/Antispyware portion solved the slowness issue.
I have a ticket open with Symantec Support and the latest recommendation is to install RU5. I guess I will give that a try and see if it makes any difference.