Placement of Search textfields and dropdown

[qmaan]

I want to add search boxes like in this forum http://prntscr.com/dxi2k6 in my website at the marked place http://prntscr.com/dxi2sk , Screen captured from http://www.suggestedcoupons.com/forum/by-retailers/a . Moreover i want to search just sub Channel names/subforum in any channel/forum or subforum.

So what is the way of customizing so.

Regards