ok - you need to hack the database back into the server. See this blog post: TechEd Demo: Creating, detaching, re-attaching, and fixing a suspect database

Yeah, the log file's corrupt - one guess would be a drive wasn't honoring write-through requests to the log file. Anyway, without going back to your backup, you'll need to...

It's possible for a page to be corrupted, by a few bits being flipped here and there, that doesn't affect the structural integrity of the records, page, or index/table the...

Gail (and others) - once a database is upgraded and checksums are enabled, torn-page protection is still in place until a page is subsequently changed - see Inside The Storage...

It would help if you explained what the trace flag does... 818 enables some code which could help with the detection of stale reads. You could also try trace flag...

This is definitely 2000, from the error messages. 2005 errors from CHECKCATALOG are completely different.

Did you create a user-defined type, and then someone mess with the system tables directly?

This might happen when a CHECKDB-created snapshot fails to be removed if something goes wrong while CHECKDB is running. Doesn't happen very often - but when it does the hidden-snapshot...

Your corruptions are 'disappearing' because the rest of your nightly maintenance is doing stuff like rebuilding indexes (i'd guess) that are deallocating the corrupt pages, and moving the indexes to...

And programming is irrelevant - you can't do anything in SQL Server that will cause corruption - see Search Engine Q&A #26: Myths around causing corruption

Yes and no. Yes, in that tempdb will be recreated and may use a different part of the drives hosted by the IO subsystem. No, because your IO subsystem still...

It's a tempdb page. You could try running CHECKDB on tempdb, but the checks are somewhat limited on tempdb, and it's likely the page isn't allocated any more and so...

This looks just like I/O subsystem corruption - the page is full of garbage.

I'd like you to turn on page checksums, which will catch when the I/O subsystem is causing...

No idea how to tell what the physical address of the pages are on the hard disk - all I can say is that the offset of a page within...

See Is running repair on msdb safe?

Just be very careful when repairing msdb - and make sure you know what repair deleted (remember that repair is basically "delete what's broken and fix up all the links")....