Vista cannot write to PortableAppsMenu.ini

Actually, every official app as well as the entire platform works on Vista without issue. I have not checked it out on Vista SP1 yet, though.

Really weird, because I have UAC fully enabled on all my Vista SP1 machines and every one of my portable apps work just fine.

First, UAC is there to warn you of potentially dangerous events -- dangerous in that they can allow international crime syndicates to install software on your machine to turn it into a spam bot or worse. Instead of turning UAC off because it gets in your way, you would do much better to figure out what is triggering it and see if you can stop doing it -- use different software, or whatever. By all means turn it off to confirm that those settings are the problem, but don't consider the problem solved because it goes away with UAC off.

Second, the problem is most likely the access permission you set up in NTFS on your XP machine (NTFS has access controls whether you want it or not). The files are most likely owned by your account on the XP machine, which doesn't exist on the Vista machine. When it checks the access level, it would deny access to you, except that you are an administrator. The Administrators group exists on all NT class machines by default, so when you go in with Explorer you get access. What I think is happening is that the RequestExecutionLevel command we use in the menu or launcher tells Windows that you are a regular user, and to ignore the Administrators group. Windows happily does so, discovers that your user account on Vista does not have specific access to the NTFS file system on your portable drive, and falls back to a group that does have access, probably Everyone or something, which has read access. (If Windows ignores the Adminsitrators group, your User account is probably pretty limited.)

The thing to learn from this is not that you need to turn off UAC, but that you need to figure out how to make NTFS work for you (or switch to FAT32). If you take that drive to a machine where you do not have Administrative privileges, you will not be able to access the drive whether or not you turn off UAC there. The only way you will be able to access the drive on another machine is if you set the drive so the Everyone group has full access, or something like that, since there is an Everyone group on all machines.

If someone has physical access to your drive, they can take ownership of the NTFS on it and have access to everything. So making it default to giving the Everyone group access isn't really going to give you much less security. The only way to have real security is to make a TrueCrypt volume or encrypt your important files.

In other words, turning off UAC lets you diagnose the problem. The problem is still there, and will reappear if you plug in to a machine where you don't have admin. If you just say "UAC is the problem" and leave it off on your own machines, you might get bitten by the "gotcha" on another machine. UAC is not the problem, NTFS permissions are the problem. Leaving UAC off just lets you get your work done on that machine, but doesn't really solve the problem, and is dangerous besides.

Does that make sense?

Microsoft didn't put UAC on Vista to make it inconvenient for people, but to allow the built-in protection to actually work for a change. Too many people run XP as an administrator, and clicking on something accidentally or waiting a few days too long to run Windows Update has resulted in millions of machines joining the spam bot army, or passwords and bank account numbers being transmitted to a crime syndicate. Most of the spam you see is sent from compromised machines where people ran all the time as Administrator. 99% of those machines would not be compromised now if they had figured out how to run as regular users instead, and spam would only be a major problem instead of an overwhelming one.

NTFS is always bound to cause issues like this if you share the drive with multiple computers. The issue here is in how NTFS security works. Basically, when you create a user account in Windows, the account is assigned an ID number. NTFS access control is implemented in terms of these IDs (I assume Linux and OSX AC work similarly): when you set the security for a file, it stores the IDs and the permissions given to each. If, on another system, your user ID (which is independent from your username!) happens to match, then you get the correct permissions. If it doesn't match, you'll likely be denied access.

Vista security is implemented so much differently when UAC is turned on that that's probably what's happened: with UAC on, even admin accounts run as standard users for most of the time and I'd guess the "standard user" half of the equation is assigned a different user ID.

Save yourself the hassle and format the drive as FAT32. I can't see what features NTFS has that you'd absolutely need. Compression is one perk I suppose, but most of the apps here (excluding the Mozilla ones because of licensing issues) have already been heavily UPXed and otherwise squashed down to size.

NTFS uses security by default which causes major issues with Vista.

You should reformat your drive as FAT32. And then convert it to NTFS from the command prompt: convert X: /FS:NTFS /NoSecurity