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If it's already dropped, then you can hand register it at any registrar.
But if it's just expired, you'll have to backorder it through Snapnames, NameJet, GoDaddy, AND Pool. The original owner has a grace period during which he/she may retrieve the domain.
If it's a highly desirable domain, you will have competition through a domain auction. If it's a must-have name for you, be prepared to pay big bucks for it.
If the name is expired (and a premium domain), it's probably not a good idea to tip the owner off that you're interested in the domain.
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