Zope is taking too much!

I have a problem with Zope,
The time for handling 5 requests is taking too much(table 1).

I think that if requests are made at the same time, their answer should be relatively close to each other, but it is not. The content is dynamic, it depends on the user. I have verified on DB blocking, and there is not such a thing.
The Microprocessor graph shows no more than 50% and there are a lot of free memory.

Does anybody know if the solution is about Zope configuration or Python programing?

Table1. Users and Time
Number  Time of Time of Time of Time of Time of
of Users User1   User2   User3   User4   User5
  1             5
  5           14        24        26       28        30

System:
Computer: Compaq Server
MicroProcessor: 2 microprocessor  pentium III 1400 mhz
RAM:  1 GB
HD:  16 GB
OS:  Windows 2000 server SP3
DB:  MS-SQLServer 2000 SP2