As a fan of the first Xbox, i was really interested by buying the Xbox 360.

However the recurrent problems(noise,lack of reliability,etc...) as well as the lack of a built-in HD drive has prevented to buy one until now.

I am waiting for the first major hardware revision of the Xbox 360 which hopefully will solve most problems(especially the noise and the reliability).

I hope that i won't have to wait for too long or i will rather invest the money i save for the Xbox 360 in the upcoming upgrade of my PC.

I prefer consoles gaming to PC gaming but a most significant upgrade of my PC(full HD monitor for example) would be overall much more useful to me. 

There have been several revisions to the xbox hardware. Mostly board and cpu improvements to deal with the heating, cd scratching, red ring of death issues, and the addition of HDMI port. Falcon, Jasper, Opus and Valhalla are the board we know of. Falcon is the one that the original xbox 360 had. Jasper will include both a 65nm CPU and GPU. Opus is a revision of the Falcon motherboard designed for the older models of the Xbox 360 - the ones which lack the HDMI port. It will implement a 65nm CPU into consoles which are sent to Microsoft for repair. Valhalla is reported to include a CPU and GPU unified into one chip, which will be manufactured at the 65nm process. So there are many improvements that have been executed.

I think most of the reliability issues have been resolved. The detachable HD is actually a good thing. Right now PS3 owners are being told to buy new HD drives or external ones because the largest they have is 80 GB. At least Xbox 360 owners have a 120 GB upgrade thats very easy to transfer information and install. Hopefully, Microsoft will get us another HD upgrade in the near future.