Try this next
Attempt No. 3: Check this website
http://windowsxp.mvps.org/AddRemove.htm for removing invalid entry in add/remove list... After this, see if installation works...
Attempt No. 4: first, backup your registry and create a system restore point. Then, open regedit, and search for the term Opera and delete all such entries one by one (you can also try out this tool at
Parhelia Tools - RT Scan Tool which will list search results and allow you to select and delete). Then, restart the system and try again...
Arun