Computer newbies forum: How do I delete extra OS and local drive?

Hello-- Please bear with a newbie

There are two OS on my computer. Everytime I boot my Compaq Presario desktop computer, it makes me "chose Operating System" and I have to pick. I have two local drives now, and the smaller of the two is the default. I have included details and circumstances of problems and their error messages below to aid in diagnosis:

I tried to download Service Pack 2. It said I didn't have enough disk space. When I went to "My Computer" to check out what was going on, I found that I had two hardrives-- a "C:\" hard drive and a "D:\" hard drive. The C:\ drive has 17.09 GB of space with 16.45 GB free. The D:\ drive has 2.93 GB of space with 17 MB free.

The first problem is that it defaults to D:\ instead of C:\. (I think my desktop may even reside on D:\)

I can't install any Windows Updates because I don't know how to tell Windows Installer to install them on C:\ instead of D:\. Everything goes fine with small updates like Hotfixes, but not large ones like SP2. The download of SP2 went fine at first, but then I got an error message saying there wasn't enough available disk space to install it.

Below are two more problems that are related to this core issue: I don't understand what's causing this, so I'll just tell you what happened by describing two incidents which I think may be related.


1-- I downloaded a Freeware Diskcleaner Utility file from the internet and saved it on C:\. So the setup file was residing on C:\. I ran the setup and got an error msg saying that there wasn't enough disk space on D:\ to install the program. This confused me because the program did not reside on D:\, and I specified all files reside on C:\ during the installation.

2-- I tried to install some Adobe fonts I need in order to print some Manuals for work. The font files were on a CD ROM disk. I tried to copy and paste them off of the disk, and onto the desktop. It said there wasn't enough space on D:\ to do this (This is why I think my desktop resides on D:\) I copied the files to the "Fonts" folder on drive C:\. But when I opened the PDF documents that needed the fonts, I got another error message saying the fonts were not installed.

I booted the computer to command prompt. It made me select a Windows OS (there was not an option to start in DOS). The command prompt defaulted to D:\. I changed directory to C:\, then tried to format D:\ but was unable. Then I did "Erase D:\*.*" It erased some, but not all of the files on D:\. Then I switched over to D:\ and tried to do erase and format C:\ with similar results. Then I rebooted the computer with my XP disk in the drive. Like always it went to the "Choose Operating System". When I selected "XP Home" (the OS I want to keep), it went to what would normally be the Desktop View. But there were no files, no Windows Explorer Bar, no start menu, etc. The system did not respond to "CTRL+Alt+Del". I restarted the machine by turning it off and on with the power button. Then I hit F8 and went to the boot menu. I selected "Boot in Command Prompt" again, and ran XP Home Edition setup directly off of my CD Rom Drive (F:\) from the cmd prompt. The setup seemed to go find until at the end, I got an error message saying that some files were not installed. It prompted me to logoff the computer and restart. It said that XP installation would complete from there. I logged off and rebooted from the cmd prompt (shutdown/l, shutdown/r). It rebooted to the usual "Chose Operating System" screen. I choose XP Home Edition. It loaded the "blank Desktop" view once more.

How do I delete the unwanted OS and extra drive? How do I reinstall XP so that the desktop view is not blank?

I don't mind wiping everything clean and starting from scratch-- but I don't know how to do that. I would really appreciate any help you can give me.

Thanks!
Adrienne