How to Enumerate/List All Installed Applications in Windows Xp

How can I enumerate/list all installed applications in Windows XP?

If you mean the list of installed applications that is shown in Add\Remove Programs in the control panel, you can find it in the registry key:

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Uninstall

more info about how the registry tree is structured can be found here.

You need to use the winreg API in python to read the values from the registry.

Registry path to find ALL the installed applications

Your most reliable option is probably to use Windows Management Interface (WMI) to enumerate the software installed by Windows Installer.

See Here
Enumerating Installed Software

Win32_Product class

Note that this does not guarantee that Internet Explorer is going to show up there. I think you can safely assume that Internet Explorer is going to be present on every Windows computer currently out there; Microsoft views it as part of the operating system.

You can, however, find out which version of IE is installed.

Detecting installed programs via registry

User-specific settings should be written to HKCU\Software, machine-specific settings to HKLM\Software. Under these keys, structure [software vendor name]\[application name] (e.g. HKLM\Software\Microsoft\Internet Explorer) may be the most common, but that's just a convention, not a law of nature.

Many (most?) applications also add their uninstall entries to HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall\[app name], but again, not all applications do this.

These are the most important keys; however, contents of the registry do not have to represent the installed software exactly - maybe the application was installed once, but then was manually deleted, or maybe the uninstaller didn't remove all traces of it. If you want to be sure, check the filesystem to see if the application still exists where its registry entries say it is.

Edit:

If you're a member of the group Administrators, you can check the HKEY_USERS hive - each user's HKCU actually resides there (you'll need to know the user SID, or go through all of them).

Note: As @Brian Ensink says, "installed" is a bit of a vague concept - are we trying to find what the user could run? Some software doesn't even write to the Registry at all: search for "portable apps" to see apps that have been specifically modified to run directly from media (CD/USB) and not to leave any traces on the computer. We may also have to scan the disks, and network disks, and anything the user downloads, and world-accessible Windows shares in the Internet (yes, such things exist legitimately - \\live.sysinternals.com\tools comes to mind). In this direction, there's no real limit of what the user can run, unless prevented by system policies.

Get a list of installed programs with application icons

To determine if its an update, there will be a key called IsMinorUpgrade. This is present and set to a 1 for updates. If it's 0 or not present, then it's not an update.

To get an icon from an executable, use this code:

VB:

Public Function IconFromFilePath(filePath As String) As Icon 
    Dim result As Icon = Nothing 
    Try 
        result = Icon.ExtractAssociatedIcon(filePath) 
    Catch ''# swallow and return nothing. You could supply a default Icon here as well 
    End Try 
    Return result 
End Function 

C#:

public Icon IconFromFilePath(string filePath)
{
    Icon result = null;
    try {
        result = Icon.ExtractAssociatedIcon(filePath);
    } catch { }
    return result;
}

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