The page where you download PIX software from (http://www.cisco.com/cgi-bin/tablebuild.pl/pix) states that you need 8Meg of flash for any 6.x code. You only have 2Meg so you'll have to purchase a 16Meg flash card if you want to upgrade.
The one that gets everyone is that they don't remove the 2Meg flash card first. You HAVE to remove this before putting in the 16Meg flash card, otherwise the PIX won't boot up. Also, when people are going to remove the 2Meg flash, the way the cabling is internally in the PIX it can look like the 2Meg flash card has the console port on it amongst others, and so people think they can't remove it. If you look closely the 2Meg flash card is the only card without any ports/connectors on the back of it, remove that one and replace it with the 16Meg card.
Also, you might want to upgrade to 5.2(x) first, then go to 6.2(x), just to make sure there's no config issues, but you should be OK.
Also, the manual says that the 16Meg card is not for the PIX-520. This is wrong, ignore what the manual says.
Re the upgrade, spending 9 bills on a card seems excessive for a firewall that is 3+ years old (already had to replace the power supply), and would total more than half the cost of brand spanking new 506e w/ 3des & smartnet. Are there used cards out there for less - didn't see any on ebay?
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...