Java 6 software can't run on Java 7, not the advanced stuff at least. Most will break, and I am angry that Java made version 7 standard, it makes a lot of older Java software break, that would work but needs to be recompiled... Anyway, rant over.
You can have several Java versions, Control Panel lets you swap between what you want to be default. Although I can honestly say I think they need to update it and give you more power, I can't swap the system version usually, gotta regedit.
Also about the bits, I wish they'd make a smart java installer so that you can specify in the argument if it's 32 or 64 bit, if you run 32 on 64 it may not work, or vice versa, it's a problem when you have DLL libraries for 3D or other purposes. It doesn't either help that locating "all Java versions installed" is not so easy either. Like me I have several but what is set to default is what all Java apps try to use, jeez.
