Well let me see if i can offer some help here...You can buy a chip that has been preflashed, it has to be cromwell BIOS though if its a "hacked" cromwell or anything else then it becomes illegal otherwise its ok, and besides most places that sell modchips will have the cromwell BIOS already on it.
DGdaPilot: As far as what u will need to do what you want with your XBOX i will give u my setup since you are kind of wanting to do the same thing so this is what i have.
Xecuter 2.3b pro MOD chip
Western Digital 200GB HDD (when you choose you HDD make sure it is "lockable")
For movies and music to be played on my BOX i use XBMC (XBox Media Center)
To play games online i use XBC (XBox Connect) it allows u to play games online and FREE

its also nice if u have games "backed up" on your HDD and want to play them online which is something u cant do with XBL (XBox Live)
With how u want to play games online here is a few things to think about in comparing XBL and XBC to help u decide what u want to do.
XBLI beleave u will have to be hooked up to your router.
Must have a "lockable" HDD and will have to be Locked to play XBL.
Must have MOD chip turned OFF or u will get baned from XBL
You can ONLY play XBL with ORIGINAL disks.Can not play games that you have saved on your HDD.
XBL does cost money (for most this isnt a problom though)
XBCWill alow u to Have BOX hooked up to your PC sence XBC runs on your PC.
Dont need to have a "lockable" HDD since it doesnt need to be locked to play XBC.
Can have MOD chip on
You can play original disks or ones backed up on your HDD
XBC is TOTALY FREE
this is just a list of comparasons of things that i know to the best of my knowlege. hope this is of some help to you, and good luck with your box.