Sell your V4 on eBay, get as much as possible for it. The buy a V7 from a friend/local paper (this way u can make sure its a V7)..
Now either practice soldering untill ur confident and give it a shot, or get someone to install it for you. I suggest getting a Crystal Chip.
Now.. If you have lots of money

Practice soldering on your V4 motherboard and sell the rest of the V4 as parts on eBay. Or even, install the chip on the V4 if it works sell it chipped, get lots of money this way. Then you can do all the above and still have money left over for more ps2 games

or even a HDD :d