[HTC Sensation] Skipjacks:
Before you do ANYTHING else, read this.

What is your current ROM now? Do you currently have ICS? If you are still on Gingerbread installing the 3.33 firmware will prevent your phone from booting into your ROM. Your phone will not be bricked, and is full yfixable, but it will not boot until you install an ICS or Jelly Bean ROM. Don't proceed with the firmware install if you are on Gingerbread until you've backed up all the data you need and have an ICS or JB rom ready to install in it's place. Otherwise this will be harder.

No. It has to match the MD5 that Kohr-Ah posted right under the download link.

This...

MD5: 07cc2a2ea4473e8fe8d6fe844c4020a1

Boot into your current rom.

Install any file explorer. ES File explorer is a great option from the Play Store.

Download the firmware file. It will be called PM58IMG.zip

Use ES File Explorer to check the MD5 sum.

Open ES File Explorer. Find the PM58IMG.zip (probably in your Downloads folder or whatever fold the app you used to download the file puts things in)

Long press the file. Little boxes will show up to the right.

Click MORE at the bottom of the screen. (Might be at the top. I'm looking at this on my tablet. It might be different on the phone version)

Then click PROPERTIES on the pop up menu

Then SHOW CHECKSUM

Selectthe MD5 checkbox.

Click CALCULATE

A long code shoudl show up under MD5 on that screen.

If it matches this EXACTLY MD5: 07cc2a2ea4473e8fe8d6fe844c4020a1 then copy the PM58IMG.zip file to the main directory of your SD card.

Reboot into bootloader. (You might have to pull the battery in order to get into bootloader since you are still on teh stock ROM.)

If your CID is good, the new firmware package will prompt you to install it by hitting the power button. This will happen in teh bootloader.

Hit the power button. Let it install. A littel blue vertical progress bar will show up in the upper right corner of the screen for each element of the firmware install.

The screen will go black and the phone will reboot back into recovery during this process. Your heart will skip a beat because you will think somethign went wrong. It didn't. Everything is fine.

Reboot when its' done and if you arleady have an ICS stock room it should boot right up. If it gets stuck in bootloop you will need to get a recovery installed first so you can wipe the cache and dalvik. That happens sometimes when you change firmware. We'll get to that later. One step at a time.

I will check in on you later, but be advised that I'm about to go home and have dinner and put my daughter to bed and all that good stuff. Check the time stamp on this post. I will be unavailable for about 3-4 hours. I'm sure there are plenty of other people who might read this thread and try to help if you get stuck in the mean time. But I'm not going to be available for immediate assistance for a few hours. So if you can't live with your phone not working for a couple hours and you're worried that you're goign to get stuck halfway through this process, wait until later before starting it.

Or start it now and if you get stuck just post the details of where you're stuck here and hopefully someone else will help you sooner.