LOCKS on n-Tier Transaction on MTS

In my case Data Keeps on updating the stock values from the Exchange to provide
uptodate Stock value Ticker information,in a SQl Sever Database by a component(VB6.0)
method deployed on MTS 2.0 with Requires Transaction Mode.
If this is going to block performance how do i impelement locks.
Or Isolation or whatever how to go about it...


Similarly another method keeps on putting orders as well as processing it same time.
This also may be many many orders as i can put orders from web as well.
But updation and reads are happenning only for main 2 tables.

It updates right now.No problem.But i fear what if many clients etc.
If this is going to block perfoemance how do i impelement locks.
Or Isolation or whatever how to go about it...