I've not used LinQ, sorry. After a quick search, I can't seem to find much specifically relating to LinQ & MsSQL together, but MSDN has some info on the syntax for LinQ (i.e. non-MsSQL-related).
You could always simply compare the MySQL/MsSQL syntax and then just change your LinQ code accordingly. From memory, it's all quite similar - but don't quote me on that as most of my clients use MySQL rather than anything else.
Edit: Incidentally, the main purpose of LINQ is to normalise the queries used to gather data from different sources, so the same queries should 'theoretically' work on SQL as work on XML, so long as the data holds to the same underlying semantics.
I suggest that before you even start working with InSim, you go and you learn how to program basic tasks like File I/O (Input/Output). Without them, you are not going to get very far.
No-one here has a problem helping you, but you must help yourself first. There are plenty of tutorials for your chosen language (in this case, C#) around the Internet. Simply use Google to search for C# tutorials.
When you can program a simple File I/O program and you've learned how to send TCP and UDP packets over a network, you'll be far more ready to start learning how to interact with LFS through InSim.