vSphere 4 Client minimum requirements are;

A.
3GHz CPU, 2GB RAM, 2GB HDD space

B.
500MHz CPU, 200MB RAM, 1GB HDD space

C.
266MHz CPU, 2GB RAM, 2GB HDD space

D.
266MHz CPU, 200MB RAM, 1GB HDD space

Explanation:
Minimum Requirements for the vSphere Client
* CPU – 1 CPU
* Processor – 266MHz or faster Intel or AMD processor (500MHz recommended).
* Memory – 200MB RAM
* Disk Storage – 1GB free disk space for a complete installation