Huh. So You're looking to install OptiFine and ModLoader?
Here's the Deal.
I use a program called Multi Minecraft, or as it's more commonly known, MultiMC. It's similar to the Magic Launcher but different.
After downloading it and doing various other things (if you need dat, go on YouTube and search up an installation tutorial for MultiMC,) you'll want to go into your MultiMC folder and double-click the .exe. Then, it'll open up the launcher. Go Up to the Upper Left Corner and click "Create A New Instance." Instance basically stands for Version. Upon clicking it, a little window will open with self-explanatory things. (P.S. Some MCRewind versions, if they're far back enough, have problems with the patches it downloads upon creating them. Dunno Why.) Anyway, if all goes well, then it'll download the .jars and all of those things. Right click your New Instance (Version) and then left-click "Edit Mods." In this window, there's a download button for Minecraft Forge, which isn't Modloader, but as tnmjimbob says, it is
way better. Then download just OptiFine from the MC Forums thread, listed here:
http://www.minecraftforum.net/topic...b4-fps-boost-hd-textures-aa-af-and-much-more/
There are multiple versions, including Light, Standard, and Ultra. The choice is up to you, but I recommend Ultra if you have a decent computer build, because then you can get into truly amazing things like Sonic Ether's Unbelievable Shaders (
http://www.minecraftforum.net/topic...rs-unbelievable-shaders-and-glsl-shaders-mod/) and incredibly high resolution texture packs. we're talking like 512 by 512 in a select few cases. If your computer is decent, but lacks a little bit in memory, GPU (Graphics Processing Unit, i.e. Graphics Card,) or CPU (Central Processing Unit, i.e. your Motherboard,) then get Standard, which will still work for probably 99.9% mods out there, but some of the aforementioned things are incompatible with it. If you have a really crappy laptop or baby computer like my old one that takes like 30 seconds to start up and barely plays Minecraft proper, then get Light. It works with even lesser mods still but you will see a tremendous amount of FPS increase. 20 fps increase and above is common.
After Installing OptiFine, go to your Windows downloads if you're using Windows Vista, 7, or 8, and drag your downloaded zipped folder or, in some mods, .jar file, to your Desktop. Then, open up your MultiMC folder again (I recommend dragging it onto your Desktop at some point or another,) and go into the folder called mods. Your downloaded Minecraft Forge via the button on the little window mentioned earlier should already be there. Drag OptiFine in as well, then go back. Activate the .exe and right-click your instance, selecting "Edit Mods" again. Your Minecraft Forge is there, but not OptiFine. Left click the "Add" button, which will take you to your mods folder. Double click OptiFine, and just click ok on everything.
That's it! Double click your instance (version) and login to experience the pure joy.
P.S. That was a mouthful.