You can build a dll using the following command line .
Assuming your command window has the appropriate path set to use the following exes:
VB.NET compiler vbc.exe
vbc.exe /out:SyncVB.dll /target:library SyncVB.vb
C# compiler csc.exe
csc.exe /out:SyncCS.dll /target:library SyncCS.cs
To reference it within the .aspx page use the Import directive:
<%@ Import Namespace=’SyncVB’ %>
or
<%@ Import Namespace=’SyncCS’ %