Subject: Can a table of p*q numbers be used to crack a pub. key encrypted message?

Hi.  I very only semi understand the public key crypto system.  I know that the 
number of primes are infinate, but the frequency at which they occur gets less 
the higher you go.  Most people therefore, when 'choosing' their primes for p 
and q therefore in practice have a limited choice, so why can't you crack a 
message simply by trying it against a table of all the possible factors of all 
the primes we know of?  oh. I have been looking just now round the web and i 
found a list of the first 98 million primes.  How many primes have been found 
then in total? (alot)? And I suppose a table of all the possible combinations 
multiplied together would be pretty long. My question still stands though as we 
haven't always known about so many primes...  Thanks! 

Re: Can a table of p*q numbers be used to crack a pub. key encrypted message?