Unless you have these two PC's daisy chained to both have a connection, you shouldn't have this problem.
If you have a setup like:
Code:
Connection (ISP) --> Modem/DSL/Cable --> Router/Switch
| |
| |
PC1 PC2
When ftp'ing, it won't pass the data thru the DNS server, its only there to tell the connection where that connection is and how to find it, etc.