Our shift from 2k5 to 2k8 and then on to 2k8r2 had trouble on the upgrades (mostly self-induced), but the performance and "add ons" were well worth the fight. The Change Data Capture (CDC) alone has been an immense tool in auditing and in some places, trouble shooting stored procedure inserts and updates. They both support "Legacy DTS" processes, though how much and for how long will require a Google search.
With each upgrade (as mentioned above) we simply detached and reattached each database after the upgrades completed. There were no complications at all with this (we did make backups just in case though).
As djj55 mentions, the longer duration of support also adds to the reasons to go ahead and at least move to 2k8 if not r2. If my memory serves me correctly, the 2k8 and r2 upgrades had tool sets for upgrading from 2000 directly (again, Google is your friend in verifying this).
While I'm a fan of Oracle, being an acting DBA in MS-SQL for the last few years and working with 2k8 and r2 have been a big improvement from the 2000 and prior versions.
SSRS (Reporting Services) is still a work in progress, it has really gotten closer to the reporting abilities of Crystal and Access reporting tools. Plus it's integrated which makes it easier to manage and doesn't need a separate server (or license) like Crystal wanted (at least the last version i used did). Tie it into an intranet and create some basic views/stored procs and let the managers create their own reports without them bugging you every month end.
If you're going to go the route of 2k8, I would highly recommend looking into r2. It cleans up some minor issues with SSRS and CDC, but also improves on performance and gives you access to more tools and options. Adding a DATE and TIME data types have also been handy.
And lets not forget.... the best feature of all for 2k8 and r2.... Intellisence for SQL. So worth it.
Just my observations.
Suggestion: If possible, Install on a separate server to test the upgrade impacts across your systems. For us, the impact was almost nonexistent, but for some could be a six month endeavor.
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Stubbornness is a virtue -- if you are right. --Chuck Noll
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