If you want to get a ca from web enrollment page on windows 2003

If your computer's version is Windows 2008 or Windows Vista, I will see this Error page.

You can fix it simply.
Download this updates and install your Web enrollment server.

[Source]
http://support.microsoft.com/kb/922706

PS.
After install the hotfix, you may configure the SSL for access the Web enrollment.
When get a certificate on the windows 2008, it can access HTTPs only.

Update for x86 version of Windows Server 2003

http://www.microsoft.com/downloads/details.aspx?FamilyId=FFAEC8B2-99E0-427A-8110-2F745059A02D (http://www.microsoft.com/downloads/details.aspx?FamilyId=FFAEC8B2-99E0-427A-8110-2F745059A02D)

Update for x64 version of Windows Server 2003

http://www.microsoft.com/downloads/details.aspx?FamilyId=B9E1A5F2-A09C-421C-84D6-BFDDBF587D64 (http://www.microsoft.com/downloads/details.aspx?FamilyId=B9E1A5F2-A09C-421C-84D6-BFDDBF587D64)

Update for Itanium version of Windows Server 2003

http://www.microsoft.com/downloads/details.aspx?FamilyId=511014E2-9717-458E-9318-77DC38D20147