Dlink router to router for internet connection

The desired connection is like this:
Desktop<--->Wireless Router A<----> Wireless Router B<---->Internet

**Router A is D-Link Wireless Router DIR-300**
**Router B is D-Link Wireless G ADSL2+ Router (DSL-2640B)**

My desktop do not have a LAN cable long enough for direct connection to Router B and no wireless adapter too. I wish to make use of the extra router (ie Router A) to make another wireless connection to Router B for internet surfing.

Please help me with a step by step guide on what to configure. Thank you.