low-level function calls, such as defragment and scandisk

Hi vb guyz. I need to know how to do the low level function calls
in VB, such as scandisk, scanmem, defragment, thin' s like that.

Thanks

For Defrag, run

VB Code:

Shell "defrag", vbNormalFocus

For Scan Disk run

VB Code:

Shell "scandskw", vbNormalFocus

How would you implement these calls?