I did this on Windows 2003 Web edition, so should work on all flavors. This allows you to get a cmd prompt without having to go through RDP.

Easy method:

"bootcfg /ems ON /port COM1 /baud 9600 /id 1"

If this doesn't work, Hard method:

c:
attrib -r -s -h boot.ini
notepad boot.ini
Edit to add entries listed below
attrib +r +s +h boot.ini

In both cases, reboot required.

boot.ini looks like this when you're done, new entries in bold:

[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(1)WINDOW S
redirect=COM1
redirectbaudrate=9600
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)WINDOWS="Windows Server 2003, Web" /fastdetect /NoExecute=OptOut /redirect

Logging in:
Download Putty.exe
Specify the IP address listed on the console page. Port = 22
(May be good idea to save the profile)
At the console window login: enter account number and port number as
ES-123456:7099
(Assuming account ES-123456 and the console page specified port 99)
Enter the password specified on the console page.
Press enter once or twice, you are presented with SAC> prompt.

Most useful commands here are
'?' (? then ENTER) - to list commands
'p' - to toggle paging (not really needed when using PUTTY)
't' - to list processes.
'i' - to fix IP address (e.g. because you cannot log onto machine via RDP because you messed up IP address)
'l' - to lower process priority (e.g. runaway process that's grinding machine to a halt and stopping RDP connecting)

'cmd' - open a command channel.
'ch -si 1' or ESC TAB 1 to switch to the first cmd channel.
ESC TAB 0 - to switch back to SAC

When in cmd prompt, a useful command is "sc" command for listing/enabling/disabling services.