HELP!!jailbreak/unlock Iphone 3gs 4.2.1 with 6.15.00

[earlzie]

hey guys i have a iphone 3gs week 41
4.2.1 (8C148a)
6.15.00
i would like to jailbreak and unlock my phone... i downloaded the 4.2.1 ipsw file and ipad file... i tried to do this a few times using pwnagetool and redsnow but either of them worked so far... if you could walk me through this that would be great thanks!

The reason I already have 6.15.00 on my phone already is that I had 4.1 n i upgraded because i couldn't use my phone in my truck and they told me i had to upgrade my firmware in order to do so... sooo i did and im stuck without cydia and an unlock

[iYeow]

Use redsn0w to put you into dfu mode and restore to custom fw of 4.2.1 ( in your PM box)
Then run redsn0w to install Cydia.
Unlock with Ultrasn0w.
If this is a new bootrom, then you have to tether boot with redsn0w.

[earlzie]

when i go through all that theres no cydia for some reason

sorry i misunderstood at first but i think i got it ... thanks

ya it still doesn't work... for some reason its not letting me install the custom bundle.. saying the files need to be compressed