Sorry for didn't provide enough information for the hardware I use.
Here are the hardware I used:

1. Intel Core 2 CPU 6600 @ 2.40Ghz (shown in General Page of System
Properties
2. 1 G RAM (DDR 2 running at 667Mhz)
3. MSI P965 Neo Series (MS-7235) Motherboard with Intel P965 Chipset
4. SATA 2 200G Hard disk Drive (No Raid)
5. Realtek PCI LAN Fast Ethernet 1G
6. Operating System: Windows 2003 Standard Edition

I hope the above information helps. The following are testing I have done:

1. When the above machine arrive, I first install the Windows XP
professional, Firebird 1.5.3 super server and a win32 application
accessing Firebird database.

2. I leave the default firebird.conf as is and run the application. It
is hard to tell you what operations are slow. I did a series of
calculation that involve connect/disconnect, select, update, delete
operation to a database. The operation tooks about 17 minutes to
finish and we are happy with the result. The test has been done for
few times and the duration for the calculation remains at 17 minutes.

3. Next, we reformat and install windows 2003 server standard edition
with Domain Controller installed and Volume Shadow Copy disabled. We
install Firebird 1.5.3 super server and the Win32 apps again.

4. Then we carry on with the test on the same database. The
calculation tooks about 1 hrs and 20 minutes to finish. That is
unacceptable outcome. It is even slower than normal Pentium 4 machine.

5. I then google to find tuning solution. And I found the
CPUAffinityMask and Classic Server stuff. I follow the
instructionaccordingly, but the operation still took more than 1 hr to
finish.

6. Next, I reformat the server again and install Windows 2003 standard
edition WITHOUT installing Domain Controller. This time the test tooks
17 minutes to complete. And this is the result we want.

From the above test, shall I conclude that it is the Domain Controller
of Windows 2003 that cause the problem to Firebird server? Or there
is anything to tune to overcome this problem.

While doing the testing, I always monitor the memory usage and cpu
usage from Task Manager. No other process occuping the cpu while the
test is doing. And there is always enough RAM during the test.

However, I encounter a strange situation. When the test is run on
Windows 2003 with Domain Controller INSTALLED. The CPU aren't always
busy with the calculation. It seems like there are some pause between
the calculation (Not bouncing either). For example:
cpu usage is 50% - 50% - 1% - 1% - 1% ...... - 50%. The pause at 1%
spend a significant amount time.

However, this doesn't happen to Windows 2003 installation without
Domain Controller, the CPU are always busy during the calculation (50%
- 50% ... 50%). No obvious pause are noticed.

Hope someone here who has similiar configuration that can do the test.