The thing to understand here is that ASP.NET cannot natively interact with
the client machine, or any peripherals attached to it...

Therefore, you have several possible solutions:

1) You attach the printer to the network instead - however, not much good if
the printer is not reasonably close to the person doing the printing...

2) You build, sign and deploy an ActiveX control to do the local printing.
This will need very careful management, as you will almost certainly need to
modify your local security settings etc. Trying to deploy this on the public
Internet is a total waste of time - don't even bother...

3) You create separate "print" aspx pages which contain only the information
you want to be printed. You may have seen something similar when e.g. you
have bought an airline ticket and you are given the option to print it -
however, this will be a manual process for the client.

4) You create PDF documents of the printouts - however, these will still
need to be printed manually...

5) You don't even try to make ASP.NET do the printing. Instead, ASP.NET
simply adds print "jobs" to a print "queue", maybe in a database, and you
write a Windows service which will poll this print queue at regular
intervals and do the printing...