I have to disagree with AB and CardboardHammer. ASP can and does handle high throughput high transactional systems quite nicely. I have built sites that handle thousands of hist per hour using ASP and MSSQL. JSP offers no performance gains over ASP.
It is true that Oracle can handle more than MSSQL, but at a cost about 8x as much. You can buy a few MSSQL servers before approaching the price of one Oracle license.
.Net or J2EE are both fine choices to migrate to. The back end (database) can be any of a number of DBs. Don't be fooled into thinking that Java doesn't limit you to a specific vendor. This is one of the biggest misconceptions that abound in our business. It all depends on how your business runs. If you have an internal IT/IS department, then the most important consideration is the cost of training the staff in new technologies. If you are already runnning MSSQL, then there is no reason to decide Oracle (or DB2, or any other DB platform) is the way to go. Business software is developed by developers to solve the problems at hand. Going to Java gives you no more freedom of choice in vendors than does going to .Net -- once you deploy your solution. The key is to get it done as quickly as possible, as cheaply as possible, without sacrificing quality, or scalability.
In short, if you have a room full of ASP/MSSQL programmers, go with .Net and MSSQL. If you outsource everything, make your choice based on cost, but remember that migrating ASP code to .Net is slightly easier (read cheaper) than migrating it to Java. And as far as the back end, migrating to Oracle (plus new lic. fees) is way pricier than leaving the data on MSSQL.