Post pics of the bike. Include a headtube shot, seatpost cluster, bottom bracket, rear dropouts, a good drive-side shot, closeups on the wheels, derailleurs and brakes.

If it's a 70's Record, it'll have the Raleigh 26tpi bottom bracket. And it'll have cottered cranks. The rear wheel will be what's called a freewheel, and the cassette will simply unscrew from it. The hub will look like the singlespeed side of a flip-flop hub. You can actually put a singlespeed cog on there, but will probably need a spacer or have the rear wheel redished. LBS can do that cheaply.

If it's from the 80's, it's possible to still have the 26tpi bottom bracket and the freewheel unless it's very late 80's.

All the above advice on replacing brake pads, cables and housings and the bearings is good; definitely do them.

Again, read the Sheldon Brown webpages. He covers everything and should be required reading for BF members. Deakins wrote a nice "how-to on the cheap" page. It's on the Sheldon Brown site.

You can redish the rear wheel and use it with the existing crankset. After you've fixed the bike up and got it rolling, you can then decide if you want to put more money into it. If so, getting a set of aluminum wheels with a flip-flop hub is the best bang for the buck. Then a new crankset or a nice used one(even better). I wouldn't get too crazy with it.