I'm also a newbie, but maybe my input will be of
some use.
Flashing ROMs is a piece of cake, assuming you are modestly computer-literate. I got my Diamond at about 3PM on Saturday, and by 6PM I was running on new OS and radio ROMs.
Go here, and read as much as you can stomach. The first post alone tells you all you
really need to know. The rest is just context... The hardest part for me was finding the reset switch on the phone. (Hint: You have to take the back off.)
You need to pick a ROM. Not easy, since it seems that finding actual
descriptions of the various ROMs is hard to do. I read through the entire threads for 2-3 of the most popular ROMs. By doing that I was sort of able to acquire the flavor of each. Sort of. I ended up going with the most recent
Juicy ROM. It seems to be a very actively maintained "bare bones" ROM. Hardly any apps are bundled in, but you get all the latest driver revisions and performance tweaks. Stuff like that. It's working well for me, but then again, I have nothing to compare it to.
I also updated the
radio ROM. (the new Telus) Some people find that to increase battery life, and/or improve reception. YMMV.
The performance of my Diamond seems fine. Which aspects of yours seem slow?
I'm sure that flashing ROMs can void your warranty, but unless you outright brick your phone, you can easily reverse your changes and go back to dead stock.
I can't believe that there aren't any streaming video apps out there that would meet your needs. YouTube comes right on the phone, and I believe people are streaming off of
Hulu. I'm not sure
how, but I'm sure you could find out.