I've only ever seen two types of tire valves, the schraeder and the presta:
You most likely have the presta, as the schraeder is the very common one found and cars and most bikes.
You can buy an adapter to use a schraeder pump with a presta valve at most high end bike shops for $1-2. Rodalink (multiple locations) definitely has them.
http://sg.rodalink.com/outlet-location/
If this is a mountain bike, you probably mean 29", not 28". That's a less common (but still common) wheel size, Rodalink will also be able to help you. (If you're talking road bike, I imagine you'd have used metric)