I dont use 4.12.6 I belive the 6 java is still a beta.
The jre1.5.0_09 is good But you must uninstall any other
first. do a search in search, for any remaining java
any probs shout

Ps.. if you cant find the java. Type "jre1.5.0_09" into Gogle

Also running to many programs can really slow down a computer. Or if you have a lot of programs on your computer. If there are programs you dont need anymore you can uninstall them. You may also have backround tasks running.