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You posed three questions. Alter Kaker and Right Wing Professor have taken a good crack at parts of these, but I'll chip in a few thoughts as well.

Coyoteman, I have a question. Can an entire skeleton can be reconstructed based on these findings? How would they go about estimating arm length and such? Would they use previous skeletal fossils to help?

The short answer is Yes.

The longer answer is Yes, but...

In modern humans there are a series of regression formulas for reconstructing missing data. And arm or leg bone can give a good estimate of stature, and with detailed study many bones can provide some clues about others; the calcaneous (heel bone) is weight bearing, so certain measurements can give some data on body weight, stature, etc. These are very specialized studies, but there are experts out there who are very good.

Now the problem; with species that are less known the error rate will go up. If there is little known about a species the error rate could be large.

The fossils in the above article are rare, but not totally unknown. There are other specimens to work with, both before and after, and by knowing the approximate date and distance between chimp on the early end and modern humans on the recent end, fossils which are along that line of descent or closely related can be studied in relation to it. But, some fossils (Paranthropus, Neanderthal) are diverging from the main line and will be more problematic; the degree and nature of the divergence needs to be taken into account.

So, to answer this question, in modern humans the technique for estimating missing data is very good, and the rarer the specimen the more error will creep in. But this is not to say its all just guesswork; it is the result of a lot of careful study. More fossils are the easiest way to get better accuracy, and in the last few decades the east African finds have been spectacular.

I have another question. it's probably a silly one. On the chart, some skulls have two branches off of them. Of those, generally one of the skulls keeps branching, and the other doesn't. Does this indicate an extinction of that line?

The dotted lines in the chart appear to indicate some uncertainty. This chart is a few years old now (2000), and will not reflect the latest finds. When a line ends, that indicates we have no subsequent fossils and assume extinction. That assumption of course can be modified with additional finds. The charts, such as I posted, are simply the best estimates very learned authors can come up with at the time; they are of course subject to change with new data.

Is the timeline determined by comparing it to other fossils, or by the strata in which it was found, or both, or something altogether different

The time period can be estimated using a number of different methods. In Africa, volcanos lay down lava which can be dated using radiometric methods. The layers themselves are usually distinctive, either with particular chemical (distinctive lava or ash deposits or the intervening layers) or fossil markers (anthing from pollen to various plants and animals). As these kinds of things change through time, the presence or absence of particular organisms can help you tell the time. Some of the dating is being done by paleomagnetism, archaeological data (including types of stone tools and other technological markers), electron spin resonance, and other newer techniques. (I don't know much about most of these.)

One part of the puzzle is that there are lots of geologists and other folks out there who deal primarily with non-hominids. Their studies are helping the paleoanthropologists in their quest to figure out the layers and dating in which the hominids are found. For every Tim White, primarily interested in the human line, there are probably dozens of folks studying other aspects of the distant past, and all can share data.

I have not studied fossil man intensely since grad school, but have tried to keep up a little. If I have made any errors, I am sure they will be corrected shortly.

From your questions it appears you are asking that evolutionists show you the reliability of their data and conclusions--a fair request! Hope all of this helps. Let me or some of the others know if you have more questions. Decent questions such as you posed always deserve an answer.