I just flashed my n800 to os2008, now before I do anything w/ installing new applications, what should i do first. I ask this question because everytime i've reflashed and installed a new app my Application Manager says: No applications installed, and Operation already in progress, and Operation failed.
So please please help me, I dont want to mess up again.

I'm starting to wonder about your wifi connection and/or ISP. Have you tried installing apps in a single environment or have you tried others?

when you say single enviroment do you meen a single connection. If so then yeah, i've only tried my home's wifi. is there a port that i should open on my router?

I doubt ports are the issue.

Before going further, I would make sure your router is set to Mixed B/G mode. That has been an issue for some users.

I would also try another wifi access point to rule out your wifi setup as the probable culprit. Post the results and we'll go from there.

This should be easy. Did you restore your programs from backup? Maybe you shouldn't have. Maybe your Application Manager Catalog is messed up. You can delete ALL the catalog items from the catalog and replace them from http://gronmayer.com/it/ to get the best repository information. (Assuming that your Internet connection is working, that is.)

If you didn't restore information from backup after flashing your device this is not relevant, so I won't go into more details now. This operation I'm mentioning is quite easy and just takes a few minutes.

^ good advice... probably more appropriate than mine in fact.

I did not back up any of my apps, for the reason that I read that they usually do not work. So its not that. But thanks anyway, I'm thinking maybe the wifi. But to be honest I've never had issues with my router as far as the wifi goes.

does having UPnP enabled on the router have anything to do with this?

It shouldn't.

All we can do without being there with you or having more detail is start eliminating possibilities. Geneven's suggestion was closer than mine to being likely, and I'm sure others will have additional suggestions. I just like starting with the "delivery service" if the tablet hardware does not seem to be at fault, since that's fundamental. A poor wifi connection/configuration can lead to a lot of issues.