Shelly,
Although I am not familiar with Simply Accounting, in my experience
there is no commercial accounting package from which you cannot export
data in some way. It may be that Sipmly uses some kind of database
behind the scenes, like SQL Server or Oracle or whatever; in that case,
you can either connect to it directly from Access, or just export in
some format. Even if direct connection is not an option, export
capability is a 99.9% certainty. It may be in Excel format (very
convenient) or at least in a flat or delimited text file, but whichever
the case you'll be able to import it in Access.
Check with your Simply support person if there is an underlying database
to which you can connect, or how you can export the data, then post back
for help with importing in Access if you need.
HTH,
Nikos