As there was a recent update for iOS 5 beta 4 and iTunes 10.5 beta 4 however many issues were resolved but still it is in beta phase means development is still in progress and somewhere else you could find issues. If you are still interested in upgrading your iPhone 4, iPhone 3GS, iPad 2,iPad 1 and iPod Touch 4G/3G than you must need to update iTunes to 10.5 beta 4, this is a prerequisite for this update.
Also you need to first update your iOS to iOS 5 beta 2 as beta 3 and beta 4 supports iTunes 10.5 beta 4. Moreover up till now there is no Untethered jailbreak tool available for iOS 5 beta 4, the only way to jailbreak your device is with Tethered jailbreak tool preferably Redsnow, which have been recently updated for Windows and Mac by iPhone Dev Team.
iPhone-Dev on Redsn0w 0.9.8b4 :
Update #4: In conjunction with iOS5 beta4 being released to iOS developers, redsn0w 0.9.8b4 is now available for jailbreak app developers (point the b4 redsn0w at the b4 IPSW). Remember, it’s a tethered jailbreak right now so you’ll need to use redsn0w to boot into a jailbroken state at each power cycle.
NOTE: It appears that by design, the OTA update that became available starting with iOS 5 beta4 will *not* be automatically applied to jailbroken devices. That’s a relief to those who don’t want to lose their jailbreak via OTA pushes. If you’re jailbroken, you’ll need to use the standard iTunes method to get to iOS 5 beta4.
Download Redsnow 0.9.8b4 [Mac]
Download Redsnow 0.9.8b4 [Windows]