VS2005 c++

I have a sln that contain 2 exe and several dll
A.exe invoke B.exe than B.exe invoke other dll

I wanna insert break point in codes of B.exe and dll  

but if I set A.exe the startup project, breakpoint in B and dll is invalid

if I set B.exe the startup project, than only B.exe runing, but A.exe is necessary for me
because lot of thing must be done by A

if set Both A and B the startup project, it's avalible to debug B, but you know
when A runing ,it will invoke another B, so 2 B.exe run at sametime ,that's not what i want

so ,any one could help me, i was really boring for this for a long time, 

any suggestion is appritate thanks