Good luck.
Most of the database vendors -- SAP/Sybase included -- give you tools to migrate from "other" competing database vendors. Similarly MS also provides you some migration tool.
The data migration -- most of the time - is easy. What is difficult typically is migrating the "logic" in form of stored procedures, triggers, defaults, jobs (being run via any number of schedulers ), applications connecting to ASE directly or otherwise (e.g. linkserver), replication to other ASE etc. etc.
If it is really a demanding application supported by ASE then do not underestimate the efforts. You will really need to throw a lot of resources and testing at it.
A couple of places I worked I have seen the migration project (ASE to MSSQL) hit wall and go up in flames due to demanding performance expected.
So good luck again.
Avinash