All existing trace flags.

Make sure you run Upgrade advisor before the upgrade.

Disable all trace flags and maintenance jobs.

Make sure your SQL 2000 is atleast have build number 2000.80.760 or later.

Backup all system and...

No need to double the disk space.

Change the Reg Key to 0 in

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQLServer\MSSQL.1\Setup\Resume

Never saw this before.Reinstall client tools.

add the account to local security policy.

Check the Local Security Policy for this ID

"Microsoft Assessment and Planning Toolkit"

is the SP3 install halting with error message "a recently applied update,KB955706 failed to install"

xx.xxx.xx.xx,1433

can you try giving port number along with instance IP.

I once had this issue and giving port number solved it.

Is this Default instance on the server?

Rebuild index and Update stats

This is again .dll file issue.

Copy BPAClient.dll file from "C:\Program Files\Microsoft SQL Server\90\Setup Bootstrap\BPA\bin" to "C:\Program Files\Microsoft SQL Server\90\Setup Bootstrap\BPA"

I ran into this issue once."upgrade advisor returned -1" this error is due to missing DLL file.

Solution for this is Copy BPAClient.dll file from "C:\Program Files\Microsoft SQL Server 2005 Upgrade...