It very much depends upon the type of leasehold that we're talking about here.
Most flats for instance, are leasehold, whereby you pay a service charge for the up keep (supposedly) of the communal areas. You, in essence, own the part of the building (the flat) for the duration on the lease - which can either a) expire or b) be extended by you.
Extending a lease is normally quite expensive depending up whereabouts you are. But for a standard 99 year lease extension, there are normally deals to be done with the freeholders.
Owning a leasehold property, with a decent length lease on it, makes little or no difference to your ownership rights and potential resale (although a leasehold house is a tad peculiar - unsual).
I'm more than willing to write you out my advice, but I'd need some more details off you.
Cheers,
Josh