I use LeadTools from Lead Technologies for all the image processing, conversion and annotation. Their are lots of options for the AutoCad viewing, zooming and plotting but only 2 real options:-

1) Autodesk's DwgX control, this requires the latest version of AutoView to run correctly. You also need to be a member of their 3rd Party Development program to redistribute it.

2) www.opendwg.org - This group contains companys such as Corel who reverse engineer the Autodesk DWG format and provide C/C++ librarys and ActiveX controls and have ASICS solid modelling in the beta test stage.

There are other DWG readers but to be honest they can be a little flaky (it's a big effort trying to keep up with Autodesk)