David,
PRO has its own site at the following address:
 
http://www.open.gov.uk/pro/prohome.htm
 
Unfortunately, their site has mostly information about how to conduct research
while there in Britain, and nothing from your period of interest directly on
line (last time I checked).
 
I recently ran across the following site listing some microfilmed material from
the PRO at Stanford, and other repositories in US (haven't checked it out
entirely):
 
http://www-leland.stanford.edu/~ceckman/pro1.html
 
Good luck, and please post or send any other fruitful leads you might
get...I've also got considerable interest in 17th and early 18th century PRO
records regarding Virginia/Carolina.
 
John Worth
Anthropologist
Fernbank Museum of Natural History, Atlanta
[log in to unmask]