To answer your questions:
First, you can only upgrade with a SATA drive, most of the links provided above are for the ATA-6 (IDE) version not sATA drives. MacSales.com is the only site that is shipping the 160GB SATA drive so far.
1 - The largest 7200 RPM SATA 2.5" drives are 100GB (this is what I have in my MacBook Pro currently)
2 - The largest drive available that is SATA is the Hitachi 5K160 (160GB 5400RPM) which should be hitting most e-tailers anytime now. You have been able to get the drive from macsales.com for a few weeks now but it is way over priced at $279. I was tired of waiting for newegg and others to get the SATA drive so I ordered one and it gets here today.
http://eshop.macsales.com/item/Hitachi/0A28844/
Seagate should have its 5400.3 160GB SATA drive out soon also, I have always favored Seagate because they make the best drives out there but after reading what Hitachi did with their perpendicular recording I am now happy to get the Hitachi b/c it appears to be a better drive. Seagate was first but Hitachi refined their perp. recording process and they have actually beat Seagate shipping the SATA version first.
I noticed a few days ago that ZipZoomFly.com has the drive listed on their site now for $179 but is out of stock. I am guessing that they will have it within a week along with Newegg.com and other large e-tailers. I am a little tempted to refuse the shipment from MacSales.com today because the drive is marked up so high ($100 over ZZF's price).
http://www.zipzoomfly.com/jsp/ProductDetail.jsp?ProductCode=100815
Also as noted above, yes, b/c of perpendicular recording we will see 200GB drives later this fall but I think they will only be 4200RPM at first.
You can check out more detailed discussion on the 160GB drives here:
https://forums.macrumors.com/threads/202117/