[Desire Q&A, Help & Troubleshooting] chrysochire:
Introductory Remarks:

- Ext Partition is only needed if your rom uses App2SD+ (Froyo app2sd works with basic Fat32 partition)

- Ext partitions are only visible in Linux = Windows can't see it.

- You can check if you have a working ext partition with Quick system info (in app market)

- On first reboot after partition, android will move some apps to the SD, this will take a lot of time. Some people have reported a bootloop on green HTC Screen, one reported a need to Battery pull 4 times before it finally worked), so be patient!!!!

Now the tutorials:

Easiest way is to install Rom Manager:

1) install rom manager

2) choose partition sd card

- 512mb ext

- 0 swap

3) let RM do the rest... ;-)

Another one is using Gparted:

(copied this from http://wiki.cyanogenmod.com/index.php?title=Apps2SD)

For a great Linux GUI alternative, use Linux 'GParted' a GUI based partition editor. (Designed for and found standard in the GNOME desktop environment, but can also easily be install in other desktop managers such as KDE and others.) Backup your SD card before you start ! The following steps will wipe the contents !

You can use a livecd of GParted, or use it from within Ubuntu (vid: http://www.youtube.com/watch?v=sVK-tJe8pXE&feature=related)

1) Connect your phone to your computer (or use an SD Card adapter...., in this case skip to 4))

2) Pull down the notification bar and mount the phone

3) Start Gparted

4) Gparted will search available drives. (Your phone should show up as a USB drive, and will be something like /dev/sdb1 or /dev/sdc1, etc..)

Warning: double-check you've not selected a hdd by mistake!

5) In the upper right corner, select the correct USB device for your phone. (i.e. check to make sure it is correct size for your SD card)

6) Right click on each partition and select 'unmount'

7) Right click on each partition and select 'delete'

If you know what you are doing, you can re-size the partitions and add a new 2nd partition formatted as ext2/3/4

8) Right click on the big gray bar (should say unallocated x.xx gb) and click 'new'

9) Enter configurations

Free Space preceding = 0

Create as = Primary

New size = [don't touch]

File system = fat32

Free Space Following = 512 (or whatever you want)

10) Click add

11) Right click on the big gray bar (should say unallocated x.xx gb) and click 'new'

12) Enter configurations

Free Space preceding = 0

Create as = Primary

New size = [don't touch]

File system = ext2/3/4 (recommend ext4)

Free Space Following = 0 (or ~32 if you want swap)

Click add

13) Click edit, then 'Apply All Operations' to write changes to disk

14) Quit GParted

15) Unmount your SD Card

16) Reboot your phone

This is what I've found so far, as the easiest method.

Another tutorial can be found under: http://androidcommunity.com/forums/f9/how-to-create-ext2-partition-14232/

or

http://xdaforums.com/showthread.php?t=534714 this is one way to do it.

What I don't know for sure:

- If the size of the ext partition matters?

- What ROMs require ext partitions?

- If Class 6 SD cards really are that important (some webpages say that class 2 cards are not able to handle ext2 partitions and end up bricked.

- How to manage the contents in the ext partition when changing SD Cards...

- How to check if you bricked your sd card...

- etc...

Good Luck