Originally Posted by JohnDThompson

I'm not familiar with "X-Speed" bottom brackets and can't find anything about them on Google, but in general, cartridges designed for square-taper cranks will have at least one and sometimes two removable cups or mounting rings. If only one side is removable, it's usually the non-drive-side and you'd start by removing the non-drive-side cup or ring and threading the cartridge into the frame, keeping in mind that the drive side threads on an English thread bottom bracket are left-hand and tighten counter-clockwise. You may find it helpful to start the non-drive-side cup after the drive side has engaged a thread or so, just to help keep things lined up. Tighten the drive side in all the way -- there may be a proprietary tool required to do this. Then snug down the non-drive side cup.

If both ends of the cartridge are removable, take them both off, slide the cartridge into the frame and start threading the cups in place to hold it. Again, a proprietary tool may be needed for this. Cartridges with both ends removable allow you to fine-tune the chainline as you tighten things up, so make sure you have things lined up properly before snugging things down firmly.