I asked this same question about a year ago. I'll share my experience since then, when I had no Altiris knowledge at all.
eLibrary - a PowerPoint presentation is read by someone who has no knowledge of the product. He or she has a wonderful voice, but is just reading a script. You cannot interact with the content, ask questions, or receive clarification. There are no lab exercises where you actually get to use the product under instructor supervision, but you may perform some click-thru simulations. If you would like a broad overview to orient you to a new product and define basic terms and concepts, but that provides no hands-on opportunities and very little in terms of seeing the actual interfaces, eLibrary training is inexpensive and will get you that.
Instructor-led training - I attended three Altiris classes with Veloce Group in Minneapolis, Minnesota. They must have done something right because the bars by my name show that I answer a whole lot of questions, even though I'm still not in production for NS7 and only use DS6.8 in production now. If Altiris is important to your company, and if you are important to your company, do instructor-led training. Personally, I viewed not training as more expensive than training.
If you do well learning on your own and experimenting, you may not need training. But you'll want to make sure your supervisor understands the difference between being trained and not trained. I presented a project workplan with training and a project workplan without. The hours I guessed I would save were not entirely offset by training, but it did make the point.
In general, the larger the client and the broader the Altiris toolset, the more important Altiris becomes and the more strongly I would recommend training. I don't work for Veloce, but I'd highly recommend checking them out. Plus, they've never cancelled a class I've signed up for, even when other training centers were cancelling every Altiris class a month before and a month after mine due to having only zero or two sign-ups.