I have tried reconfiguring the xserver, but
i can't get a better resolution. I have an nvidia graphics card. I need 1440x900 resolution. Now, all I can get is 1024x768.

Slackware is running over ubuntu in virtual box.

I am a beginner to Slackware, but not linux.

Have you installed the guest additions?

what are guest additions?

I installed off the DVD. I haven't added anything.

Guest additions are a VirtualBox creation that allow higher resolutions to be used (among other things -- I think you also need them to have seamless mouse integration). I'm not sure if they work with Slackware or not, but try starting the Virtual Machine and clicking Devices>Install Guest Additions in the menu. No OS will be able to achieve good resolution in VirtualBox without Guest Additions being installed as far as I know (I had to install the Guest Additions for Windows to use a high resolution in VirtualBox).

The guest additions are part of VirtualBox. To install them, open the virtual machine, go to the Devices menu in your virtual machine (exit from fullscreen mode to see the Device menu), click on Install Guest Additions. You should then have a new CD loaded in Slackware which should show up on your desktop. Open a konsole, su to root, cd to the mounted CD directory, and then run sh ./VBoxLinuxAdditions.run.

That'll install a few components that'll improve your virtual experience, including seamless mouse integration, as well as a new graphics driver, which should allow you to achieve a higher resolution.

Where is the image mounted? How do I get to it in terminal.

actually, it won't mount. I get this error when I try.

A security policy in place prevents from sending this message to the recipient...

Try /mnt/cdrom or maybe a folder in /media. In an OpenSuse guest it appeared as "/media/VBOXADDITIONS_1.5.7_28266" upon automounting it, but that will change depending on the version of VirtualBox you are running. To get to a terminal in Slackware, it depends what window manager you are using. If you are using KDE, click the "K" menu, then go to "System">"Konsole". That'll open a terminal for you. If you run another desktop environment/window manager, tell us which one. If you can get a "Run" box to pop up, just run the program "xterm" and it should work (although xterm is not my favourite terminal). su to root (type `su`, then enter your root password when prompted) and navigate to the CD directory. Type `./VBoxLinuxAdditions.run`, as stated above.

Raccoon1400, that error is because you haven't added your user to the proper groups. Read the sticky about HAL at the top of this forum. In short, you must add your user to the plugdev, cdrom, audio and video groups. If you don't want to get automounting of cd images working, you could `su` to root and type `mount /dev/cdrom /mnt/cdrom` (make sure that the /mnt/cdrom directory exists) and then navigate to /mnt/cdrom and install the guest additions from there. Then, navigate out of /mnt/cdrom and type `umount /mnt/cdrom` and the CD image will be unmounted. I would recommend getting HAL setup properly though, just so you know more about what a standard Slackware install constitutes.

I mounted it in /mnt/cdrom/

I can see the file, but I can't figure how to run it. I click on it and it opens in KWrite.
I tried running it in terminal, but when I try running it like I would in ubuntu, it says bad command or filename.

As root.

I got it installed. I can now get 1280x1024, but i need 1440x900(widescreen) I do not have an option for it under configure desktop.

Raccoon1400, I don't know if it's possible. Try going into fullscreen mode and see if it automatically adapts (or see if there is now an entry to configure the desktop). In real Slackware you can just edit /etc/X11/xorg.conf, but I don't think you can do this in VirtualBox without screwing it up completely. VirtualBox presents a fake graphics card to the guest OS, and hence it may not support 1440x900 resolution. A best-case scenario would be if I were totally wrong, a worst-case scenario would be if I were right.

Got it!!
I added the 1440x900 mode to the config file
I was using the vesa driver, so I reconfigured X to try to get the nvidia one. Didn't work, so I went back to vesa.
The 1280 option disappeared, so I installed the additions again. Now it will go fullscreen!
Thanks!

Although your physical computer has an nVidia graphics card, your virtual machine has the VirtualBox virtual graphics adaptor (just like it has a virtual hard disk, virtual network card, virtual sound card etc.). Thus, the nVidia driver is not the correct one. Also, you won't get any 3D capabilities in your virtual machine because the virtual graphics adapter doesn't support it.

In fact, just about the only part of your physical machine your virtual machine accesses directly is the CPU. VirtualBox does it with some clever coding.