Dynamic disk conversion imvolves deleting the volume (partitions) on the drive and starting again. If the disk is not your primary (Operating System) hdd, then backup all data on it before proceeding
If it is you boot disk with your o/s on it, you would be looking at a full re-install of windows and all your programmes:
Step by step:
To change a dynamic disk back to a basic disk:
1. Back up all the data on all the volumes on the disk you want to convert to a basic disk.
2. Log on as Administrator or as a member of the Administrators group.
3. Click Start, and then click Control Panel.
4. Click Performance and Maintenance, click Administrative Tools, and then double-click Computer Management.
5. In the left pane, click Disk Management.
6. Right-click a volume on the dynamic disk that you want to change to a basic disk, and then click Delete Volume.
7. Click Yes when you are prompted to delete the volume.
8. Repeat steps 4 and 5 for each volume on the dynamic disk.
9. After you have deleted all the volumes on the dynamic disk, right-click the dynamic disk that you want to change to a basic disk, and then click Convert to Basic Disk.
NOTE:You must right-click the gray area that contains the disk title on the left side of the Details pane. For example, right-click Disk 1.
Step 1: BACKUP ALL YOUR DATA!!!
Next, read this thread for helpful information.
Yes, backup your data first.
Here is the Microsoft guide to do that (although the article is intended for Windows server 2003, it can be useful here).
This Microsoft article has another procedure to do the conversion (don't pay attention to the article's title, and look for the "workaround" section).
You might want to take a look at the following article also:
How to non-destructively convert dynamic disks to basic disks.