To use dbcc checkdb repair options, you have to set the DATABASE, not the SERVICE to single-user mode.
Starting sqlservr.exe -m, as above, does not quite do the trick.
try this:
Use master
go
sp_dboption dbname, single, true
reference: http://support.microsoft.com/kb/264154
(ought to be updated to show use of "alter database" - i'll leave that to an expert)