Hello Gurdip,
This is purely a marketing answer. There is a difference between minimum requirements to run the software and acceptable requirement.
Aditya,
Since you are asking this question, can I assume that you don't have all your machines running with at least 1GB of RAM and the latest OS?
Here's my experience since I have a mix of WIN98, WinXP, Vista, Server 2000 and 2003 running on eScan.
Let's say that if you have 256MB of RAM as stated in the marketing material, eScan will still run as long as your users are acceptable with a 5 min startup of Windows XP and a 3 min startup of Outlook email client.
My users weren't accepting the longer startup times, therefore, the moment I installed eScan, I practically had to upgrade ALL machines with 256MB to 512MB (I would consider 512MB as a practical minimum requirement).
One more thing, I did not turn on ALL the scanning policies for eScan. I kept Ant-spam, firewall and Privacy controls off. If you plan to do that, your machines will definitely run slower than mine.