Please provide some sample code/VBA Code to link the test case in Test Lab with the acrive defect.
Also how to access the properties/different fields of the TC in Test lab
1. Log in to QC
2. Click on Help
3. Select: Documentation Library
4. Open the HP Quality Center Open Test Architecture API Reference
You'll find code samples in there specifically related to Defect links.
For your second question you'll need to provide more detail about what you're trying to achieve. I suspect a search of these forums will give you what you're wanting.
... just another Tester ...