Generate 5000 records in 2 columns of random number that being unique

How I can generate 5000 records in 2 columns of random numbers between 1 and 100 that being unique.

For example:

 A            B
----------------
 1            98
 1            23
 37           98
 6            56
 93           18
 .            .
 .            .
 .            .

thanks