and what 'no external dll should be used' means? In that case you can't just use VB, because VB needs at least the vb runtime library, so that leaves only straight C language (using only the standard i/o) How you transfer data to/from an access database without using "any" library sounds a bit extreme to me...
As for the memeory managment, 1GB is not a problem. But if your app must run in a "specified memory" space (BTW in which kind of computer/operative system wil run), well I do not see how you can do it in Windows!
Marco