Adobe Photoshop CS5 installation problem

I recently download Adobe Photoshop CS5 software and install it. But the problem is, I can not use this software. Whenever I run this program my PC become very slow and I can't do anything.
My PC configuration is- Microsoft Windows XP SP2, Intel Pentium 4 CPU 2.40 GHz, 256 MB of RAM.
Can anybody tell me what is the problem and what can I do?
