Amir,
Microsoft makes a text-to-speech tool for developers called Microsoft Agent. Microsoft Agent can be downloaded for free from Microsoft's page, but it is not stand-alone and must be accessed by another program. There are many freeware text-to-speech programs that use Microsoft Agent available on the Internet. You can go to www.cnet.com for a list. The best one that I found is called Talking Box. I don't think the program is optimized for blind users, however, since it requires the user to select the text they want read.
Just today I found out about a program made specifically for reading text in Excel and Word called Sound-Proof 2000. I've included a link to a page with information about it. This program is not free, however, and the Excel and Word versions are separate.
Finally, there's a company called Lernount & Hauspie that specializes in text-to-speech technology. You can check out there website at www.lhsl.com.
I hope this helps,
-Ben