How to diagnose network speed issues in a Microsoft environment

I have inherited a Microsoft network / environment with all of the usual culprits: Active Directory, Exchange, Terminal Server, 50 clients, File & Print Server – standard enough office essentials.

The clients are all in the 172.25.51.* range and their download speeds from the internet are a fraction of those which the servers experience. File transfers between machines in this range seem zippy enough. (See output from machine #1 – Client below.)

The servers are all in the 172.25.24.* range and their download speeds from the internet and file transfers between each other seem fine (see the output from machine #2 – Server below).

File transfers between the two ranges seem quite slow too. I guess my question will eventually lead to another but here's what I need to do first: how can I set about formally diagnosing why the clients in the 51.* range experience such terrible download speeds from the internet and the 24.* range?

I suppose the fact that the internet comes in via the 24.* range explains that slowness so my real problem which I need to diagnose and find a cause for is what is causing the slowdown between the servers (24.) and the clients (51.)?

I'm fairly certain that it's not the cabling although I would welcome suggestions as to how I can prove that it isn't the problem? It was done by a professional company so I am inclined to believe it is a configuration issue somewhere. Any suggestions would be most appreciated.

#1 – Client

ipconfig

V:\>wget ftp://ftp.heanet.ie/mirrors/videolan/vlc/0.9.9a/vlc-0.9.9a.tar.bz2
--2009-06-30 19:33:30--
ftp://ftp.heanet.ie/mirrors/videolan/vlc/0.9.9a/vlc-0.9a.tar.bz2 
   => `vlc-0.9.9a.tar.bz2'
Resolving ftp.heanet.ie... 193.1.193.64
Connecting to ftp.heanet.ie|193.1.193.64|:21... connected.
Logging in as anonymous ... Logged in!
==> SYST ... done.    ==> PWD ... done.
==> TYPE I ... done.  ==> CWD /mirrors/videolan/vlc/0.9.9a ... done.
==> SIZE vlc-0.9.9a.tar.bz2 ... 17500620
==> PASV ... done.    ==> RETR vlc-0.9.9a.tar.bz2 ... done.
Length: 17500620 (17M)

100%[======================================>] 17,500,620  39.3K/s   in 7m 35s

ipconfig /all

Ethernet adapter Local Area Connection:

Connection-specific DNS Suffix  . : domain.local
Description . . . . . . . . . . . : Intel(R) 82566DM-2 Gigabit Network Connection
Physical Address. . . . . . . . . : 00-1E-4D-F4-35-57
Dhcp Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
IP Address. . . . . . . . . . . . : 172.25.51.77
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 172.25.51.1
DHCP Server . . . . . . . . . . . : 172.25.24.10
DNS Servers . . . . . . . . . . . : 172.25.24.18
                                    172.25.24.12
Primary WINS Server . . . . . . . : 172.25.24.18

#2 – Server

wget

V:\>wget ftp://ftp.heanet.ie/mirrors/videolan/vlc/0.9.9a/vlc-0.9.9a.tar.bz2
--2009-06-30 19:41:15--
ftp://ftp.heanet.ie/mirrors/videolan/vlc/0.9.9a/vl.9a.tar.bz2
   => `vlc-0.9.9a.tar.bz2.1'
Resolving ftp.heanet.ie... 193.1.193.64
Connecting to ftp.heanet.ie|193.1.193.64|:21... connected.
Logging in as anonymous ... Logged in!
==> SYST ... done.    ==> PWD ... done.
==> TYPE I ... done.  ==> CWD /mirrors/videolan/vlc/0.9.9a ... done.
==> SIZE vlc-0.9.9a.tar.bz2 ... 17500620
==> PASV ... done.    ==> RETR vlc-0.9.9a.tar.bz2 ... done.
Length: 17500620 (17M)

100%[======================================>] 17,500,620   510K/s   in 28s

ipconfig

Ethernet adapter NIC:

Connection-specific DNS Suffix  . :
Description . . . . . . . . . . . : Intel(R) PRO/1000 MT Network Connection #2
Physical Address. . . . . . . . . : 00-11-54-31-32-50
DHCP Enabled. . . . . . . . . . . : No
IP Address. . . . . . . . . . . . : 172.25.24.17
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 172.25.24.1
DNS Servers . . . . . . . . . . . : 172.25.24.18
                                    172.25.24.12