PostgreSQL 7.4 Or SQL Server 2005 Or SQL Server 2005 Express For VB.NET And ASP.NET A

I am faced with the following dilemma: I have a Windows desktop application developed in Visual Basic .NET, it's a fairly large size, about 100,000 lines of code. I developed it in Visual Studio .NET 2003 and I recently converted it to Visual Studio 2005. My database is PostgreSQL 7.4. I have roughly 500 database objects, i.e. tables, views, sequences, and functions, in it. My biggest table probably has a few hundred thousand records in it.

Another developer in my company will soon be starting work on a Web application that will be pulling its data from the same database as the above mentioned Windows application. So basically we have a situation where two different applications, a Windows and a Web one, have to access the same database.

Currently the plan is to develop the Web application in ColdFusion. However, since I already have a large-scale application in VB.NET that will be accessing the same database I was thinking it might be a better idea to develop the Web application in ASP.NET, seeing as how ASP.NET is VB.NET. That would present more opportunities for the two applications to interact with each other.

And in that vain, my dilemma is this, should I switch my database to SQL Server 2005 or should I stay with PostgreSQL? I am happy with PostgreSQL so far but if I have one VB.NET and one ASP.NET application, doesn't it make more sense to have SQL Server database?

I know that PostgreSQL is free and SQL Sever costs money, but what about SQL Server Express 2005? That's free too, but how much of the functionality of SQL Server 2005 does it support? The organization I work for is small and it would be hard to convince management to spend money on a commercial database like SQL Server 2005 when what we have works just fine.

Any advice would be appreciated.