When you download a CentOS DVD ISO file (for example: http://iso.linuxquestions.org/download/1274/2996/ftp/mirror.its.uidaho.edu/CentOS-5.5-i386-bin-DVD.iso), it can be helpful to check the files checksum against the download list to confirm the integrity of the file.
This check is important both for security (so that your receiving a unmodified CentOS installer) and to make sure the ISO has not been corrupted during the download.
To check a CentOS DVD checksum:
1. Download the CentOS md5sum.exe tool from: http://mirror.centos.org/centos/dostools/md5sum.exe
2. Save the file to the root of your C:\ drive or to your c:\Windows\system32 directory.
3. Check the CentOS download page here and note the valid checksum, for example: 48c158fb9446148432a07634b2688915a279580
4. Download your CentOS ISO file.
5. Once the download completes check the MD5 sum:
c:\md5sum.exe CentOS-5.5-i386-bin-DVD.iso
And confirm that the sum on your machine matches the sum listed on the download page.