Since the original movie has a different take on Ra - an alien masquerading as human but not using one as a host - I figure the series and movie premises have already diverged in a crucial way. I'd take the pilot episode of SG-1 as the premise but recast or change the characters.
It would be fun to give some of the original actors new roles. Christopher Judge as a Goa'uld, Colin Cunningham as a somewhat slippery Tok'ra...