In converting between the two database types, there SHOULD be few
problems. However, notice that I said "should" in really big letters.

A. V. Roe of the AVRO Aircraft comapny had one rule -- never put a new
engine in a new airplane.

This sounds a lot like that situation.

MAKE EVERY EFFORT TO PERSUADE THE HIGHER-UP THAT IT IS DOABLE BUT THAT
IT HAS PERILS, AND THE RECOMMENDED APPROACH IS TO PERFORM A PILOT
PROJECT TO:
1) determine the approach to be made to transporting the application
code from the old to the new environments
2) determine the optimum configuration of server and database to suit
the new hardware and software
3) determine the approach to transporting the data from one system to
the other (backups are probably incompatible, so you need a transport
strategy.) BCP is the favoured apprach but the bcp's may need to be
staged (order of files as well as large amounts of data in smaller
chunks)
4) determine the extent of removal and pruning of historical data that
really isn't used much and is clogging the ssytem.
5) determine how to manage change-over from the old to the new system.
6) BIG ONE!!! Determine the imcompatibilities of the two database
servers. 99% of the base assumptions on MS will match up with Sybase.
You need to run the new installation in parallel with production to
verify that ALL PROCESSES are working and generating the same
information.

On any schedule proposal, be pessimistic and stick to them.

I've done a couple "no-problem" conversions that went off like
Chernoble.

Now much older, sadder but wiser....