my parents-in-law recently had their parquet oak floor repaired (had been hidden for years under carpet) and a local french polisher did for them. cost �500, but you could probably get this done more cheaply as some of theirs needed replacing). the guy sanded it all down with a circular sander, then finished it all with manual sandpaper in places before applying various coats of varnish and stain to bring the full colour up. it looks amazing now.
have just bought a 1920s house myself, and was pleased to find the original parquet floor in our hall, so will be using the same guy!