Hi busmech,
Yes, there are 6 holes that are to be used to screw the motherboard into the metal standoffs of the case.
"Isolating Screws": I have heard of people doing this (ie. putting washers between the mb and screws). Here's my take on this.
I have read a lot of so-called 'computer installation' guides on the net, including AMD's guide on their site, and they do not mention anything of using washers. It's just a simple 'screw the mb to the standoffs with the screws'. To the best of my knowledge, this is the proper procedure (isn't it nice that mb manufacturers like MSI & Asus, make no mention in their manual of the actual installation of the mb into the case).
So, go right ahead and install your CUSL2 using your case provided standoffs and screws (6).
Note1: you will notice a silver-coloured solder ring around the 6 standoff holes. Although mboards are probably designed to have screw heads larger than the solder rings installed without problems, the screw head should not be larger than the solder ring, otherwise you could short or damage your mb. Make sure to line up your mb properly in your case to (hopefully) achieve this. This shouldn't be a problem though.
Note2: The holes without the solder ring are meant to be used with 'plastic', not metal spacers. This is to give the mb additional rigidity in areas of high stress on the mb. I've seen a lot of modern cases that do not include the necessary case cutouts to install these spacers. It seems that these type of supports are dying. I don't think it's even part of the ATX specification, but I may be wrong. I wouldn't worry about not having the case cutouts to match these holes. They might have been more of an issue for slot CPUs, but even then you could install the CPU outside the case, not to mention the mb is able to take reasonable stress. One is by the ISA slot, and the other is to the right (corner) of the DIMMs.
Note3: I recommend installing the CPU and memory outside the case. No big deal for the CPU, but DIMMs can be tight/difficult to insert (relative to peripheral cards) and it's nice, but not mandatory (as I said, mboards are designed to handle some/reasonable stress), to have a flat surface for support when installing the memory. Just be careful to not touch the memory with the screwdriver when you install the mb.
Regarding a burn-in: Well, what I would do is run some 'intensive' benchmarks/programs. Examples are Q3A looped timedemo, 3DMark2000, SysMark and many others. You could also run Sisoft Sandra and HDTach to gauge your memory and hard disk performance.
Edit: Just to add one more thing: I'm not entirely sure what role the case screws play in electrically grounding the mb. There are ground pins on the mb ATX connector. Perhaps someone can shed some light on this. Either way, you should be fine using the screws without the washers. Just take note of the screw head width as above.
Regards,
Al