What is CPU you are having? P4 or celeron. (Specifications from DELL site)
How much RAM your system has??
Check your system configuration here.http://windows.microsoft.com/systemrequirements
Download & Run Windows 7 Upgrade Advisorhttp://www.microsoft.com/downloads/details.aspx?FamilyID=1b544e90-7659-4bd9-9e51-2497c146af15&displaylang=en
You must have atleast 1GB RAM & 2GHZ processor with Graphics Support to See windows 7 for least performance.
According to your system specifications,You can Install 32 bit Windows 7. But Drivers may cause some problem. You Can download them from manufacturer's site, not from DELL.
No Windows 7 support provided for Dimension 1100.