Mike's list is good one to go, here is my kip:
1) Whether the target server(s) will be on the same domain(s) as the current production boxes, and how this will affect the transfer of logins/DTS;
As long as the SQL account used from SOurce to target has permissions between the servers the process shouldn't have any issue. By default it will use the Service account and if they are dfferent domains then make sure to use similar account between these 2 servers.
2) Whether the network can handle a .bak file of 100Gb (last time I tried just 10Gb, the backup failed!)
Are you trying to copy the file using Operating system process or performing the backup straight away from SQL Server to the disk.
3) Whether to use the Copy/Transfer database utilities (if same domain) or backup/Attach (or is that Detach/Restore?!?!) with the consequent possibilities of having to recreate logins/users/packages.
No criteria to use copy or attach method, by experience I prefer to use BACKUP or ATTACH method. Packages and logins better to script them and apply on target server.
4) Handling cutover, as the size of the OLTP data will doubtless change if the systems are currently live.
If you need to test the new server as a pre-production until you are satisfied then you can run them parallely to see what is activity, make sure to restore the database overnight between the servers. Once the complete daily & weekly processes are completed then 1 fine day take full backup on source and restore on target then switch 2000 box.
Also I refer to the FAQ &* GOTCHAs in Upgrade on my blog - http://sqlserver-qa.net/blogs/tools/archive/2008/01/22/upgrade-blurg.aspx link.
HTH
(ps I'm going to blog this post too
)
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Satya S K J 
Knowledge is Power, you will gain by sharing it.
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