one way is to track what numbers are generated and save them in an array for instance. then check back to see if it is already generated.... IMHO if you have a range of over 50 then the numbers are going to still be random and its unlikely to get repeats. you could always get two random numbers in succession and multiply / add / whatever so that the combined numbers vary a bit more.

put names in an array, generate random numbers from 0 to the size of the array - 1. make sure of no repeats and then store the numbers in a separate array so you might have:

"Bill"
"Bob"
"James"
"Chris"
"Thomas"

so you would generate numbers from 0 to 4 and might get:

3
1
4
0
2

in a separate array. Then copy across from the string array the string at the index specified by the second array. Then it becomes:

"Chris"
"Bob"
"Thomas"
"Bill"
"James"

Hope this helps