Messed up my Vista with the partitions

Currently I am using Windows Vista Ultimate Edition with four partitions on
my Hard-disk (20GB x 4 - NTFS):

Problem: 1. Most of the programs on my Vista are not working (including IE)
2. On start up it shows the option to boot either from "Earlier version of
Windows" or "Vista", though I had formated the partition of the earlier
version (Media Center). If I do select the Media Center it shows an error of
missing files and restarts.
3. I want to merge 2 of the partitions as a system partition.
4. If I boot from the Vista DVD and approach the installation/partitions
(drive selection) part it shows an error 0xE0000100 and restarts.

Under disk management it shows up all 4 drives as follows:
C: (Healthy) System
D: (Healthy) Logical Disk
E: (Healthy)
H: (Healthy) Boot
The vista is installed on the H drive.

Please suggest me a way out...thanks in advance
Pratyush