Mrs. Lynne wants to know how she can download software and be certain she's not getting something malicious.
There's no way to be certain, but a few precautions can reduce the chance considerably.
Another option: If you know what program you want, go to that program's own site. Unless the program itself is malicious, it's not likely to be infected there.
If you browse with Firefox 3, you've got added protection. The browser scans downloads--using your own anti-virus software--before it lets you get to the file.
And speaking of your own anti-virus software, always keep it up to date. It should--and in most cases probably will--stop you from opening anything evil.