Renewing is generally not a problem at all, you 
can renew your domain any time.  There is one 
company these days though, that will moniter a 
registered domain for you, and as soon as the 
registration slips they buy it up for you.  At a 
modest fee, of course.

When I found that this was possible, it made me 
very nervous for my domain (I'm faaaar too fond 
of my website) so I went ahead and registered my 
domain through 2010.  It gets cheaper the longer 
you register ahead for it...