Question: Sometimes I download an app but it fails to download or install. The message just says that, no further details. It generally seems that the app never installs after that. Is there anyway I can find out more details about why it failed? Is there any good way to get stuff to install after this has happened.

I am using Android 1.5 on a T-Mobile Pulse/Huawei U8220

Answer: 
When this happens to me there's one thing that helps every time:

Open the Market and go to the Downloads section, then perform a long click on the stalled download. Cancel the download from here. Now you should be able to reinstall / update the app.
Does the OS actually tell you it failed to download, or do you just notice? When i was running 2.0.1 i noticed a particular problem with trying to update/download multiple apps at once. If you are doing synchronous dls try one at a time.

Another option MAY be to try using Appbrain. It is an alternative installation app that hooks into market. (http://www.appbrain.com/)

Speaking of which, you could also try your QR reader and try to install via the internet using the programs' QR codes.