hum , well, nothing fancy. You just must grab a "debug" version of Dosbox. Browse their forum, as it's spread unofficially.
Once you have that, use the debug function "memdumpbin" like :
memdumpbin 0000:0000 100000
and you'll get a 1Mb raw data file of the memory starting at this address 0000:0000, stored in the Dosbox directory.
Adjust for your needs.
Not sure I was clear on this one, but ... tell me

Sylvain