Still possible to upgrade to 4.3.3? Or use green poison 4.2.1?

[Hungryghost]

Hi everyone new to forum. I dont know much about conputers etc but I have always found forums the best way to learn about new subjects, so here goes:
I've owned an iPhone 4 for a couple of months and I have decided I need to jailbreak it. It came with ios4.2.1 and foolishly I have held off updating it to ios4.3.3 in the mistaken belief that this would make it easier to jailbreak.
Now that I actually start to look into it I have realised that jailbreakme 3.0 would have been ideal but this doesn't support ios4.2.1 yet. I want to update to 4.3.3 using ipsw download but have so far been unsuccessful. (at first I didn't realise you needed to rename .zip to .ispw) Are apple still signing ios4.3.3 as of today? Do I need to put it in DFU mode?
That's my first question, my second is if I jailbreak using greenpoison on ios4.2.1 I need to put it in DFU MODE, will this cause me to lose all photos and music and apps on phone?or will I just be able to sync with iTunes to get them back? I'm particularly concerned about some photos of my children I I have in a time-lapse app; the normal photos I can just save to computer.
Final question; what about these SHSH things? I need to save them right? What will this do?
Thanks in advance to anyone who takes the time to answer my questions.

 

[Gregoris]

greenpois0n works for 4.2.1 but no other newer firmwares

 

[Hungryghost]

Ok, well I have done green poison on my 4.2.1 now, given up on trying to update to 4.3.3 thanks anyway