You don't give much information about your environment, but as a general rule, I would strongly recommend that you use a separate folder for each MSI, and use a standardised naming convention for the folders (and for the MSI files) that gives you an immediate indication of what version of the application you are dealing with.
Your example of adobe photoshop, would recommend a folder name of Adobe_Photoshop_CS3 (or whatever version it is) and the same for the MSI name.
Otherwise, if you just use numbered MSI files, you will find it impossible to check quickly, which one is which application. At the same time, if you have two MSI's with an external CAB file, called data1.cab (this is quite a common name for an external CAB), how will you manage the conflict if the MSI files are all in the same folder?

I usually use a folder structure like:
Vendor
   ProductName
      ProductVersion_LanguageCulture_InternalRevisionNumber

ex.
Microsoft
    Office Professional Plus 2007
      12.0.4518.1014_enUS_01

thanks ,guys

en,i think use First Char is a good method.

ex.
0-9
7ZIP

A
Adobe reader 9
adobe photoshop cs4

B
big A
big B

C
creator9
citrix