Well Said.

I'd like to also vouch for the this;
as far as we know in this corner of the galaxy, carbon based is the thing. and as stated - the way these molecules combine may have influence on the structure/organization of a life form body. im not all too familiar on that area.

But, cameron has a good point, what we "SEE" as these aliens may in fact not be their true FORM, and for MANY reasons.
firstly take into consideration that we cannot comprehend higher levels of existance, not being as physical as we are, that kind of thing. also take into consideration what was said - that these higher, more intelligent Aliens/Beings can in fact manipulate things very well, including DNA. some of these Aliens, it seems all they do is engineer DNA they are Code-Freaks like that. and ill bet these are mostly the Aliens that look at twisted and wierd, like the Greys and such. Also consider screen memories flaws, and also that these nonphysical beings may project and image to display as themselves kind-of-deal.

oh really? how about you try walking on all Fours right now ?

the main keyword here is *intelligent* lifeform, not just an animal lifeform. i understand where you're coming from NeoMatrix, that all fours is more stable etc.... but that is talking about just regular Animals. Ideally Intelligent lifeforms should have some appendages to work with, to MANIPULATE tools, which some anthropologists claim is the birth of Intelligence, (i dont believe so)

But hey, they say Dolphins are quite intelligent, so that throws out my idea !?!!! haha.

but yea, i think looking into Carbon might yield some answers..
z

For instance, they say that volcanoes are not "connected".  While this is not known, scientists do not have empirical evidence so they feel there is no reason to believe it.  So, while they "assume" there is no connection, this is stated as fact.

They don't study what they do not already believe so have often been caught with their pants down. 

http://www.copernican-series.com/wswwintro.html

http://www.amasci.com/weird/vindac.html

well on different planets lets say there is no abundance of Oxygen, and mayber there is an abundance of lets say Chlorine or something. And because everything is murky and u cant see ish, or lets say u can, but in order to see they have weird eyes that only see through chlorine or some shit. and because of the abundance of a chemical lets say sulfur, everthing will revolve around it etc etc. basically the only way they could have evolved to be reptiles was if they lived on a planet which was exactly like earth.

People teach evolution is some schools.  They also teach creationism.  Somewhere in between, and including genetic manipulation of the highest caliber, is closer to reality.  With the right technology, beings can create other beings to look like just about anything, anywhere, and at any-time.  Environments can and are controlled or influenced by consciousness, as is everything at some level.  On a larger sense, the interconnectedness and multidimensional nature of reality dictates that everything can be seen to have been 'seeded' -- again on one level or another -- by a more aware aspect of the God.

What ideas did the scientists come up with for how other life forms could get round these obstacles?

well, 2 arms and 2 legs is extremely ideal for an intelligent lifeform.
at least in this corner of the galaxy  ?

Actually it is anything but ideal. Four legs creates a much more stable bodily posture, and doesn't put as much pressure on the spinal cord. This whole idea that aliens *couldn't* resemble us at all is absolute bunk, however.