SBS Performance Problems

Our company currently is running SBS 2003 Standard R2 on a Pentium D 3.0ghz / 4Gb DDR2 566Mhz / 2 NIC Config… Other than acting as our Domain Controller it is our FTP Server…

Since setting up this box I have noticed our network speed has slowed considerably… Do you have any idea’s… I personally think it has to do with the way SBS sets up DNS… Unfortunately I do not know how to fix the problem even if it was can anyone help…