In his recent webmaster video, Matt Cutts says that there’s no need of having a separate IP address for each country-specific site. The video is an answer to the question:
“For one customer we have about a dozen individual websites for different countries and languages, with different TLDs under one IP number. Is this okay for Google or do you prefer one IP number per country TLD”?
Cutts said that in an ideal world, it will be great if you can have separate IP addresses for .com, .co.uk, .fr and have them placed in UK, France or Germany. But in general, as long as you have different top level country code domains, Google is able to distinguish between them. So, you don't have to put them all on one IP address. Google does take the TLD as a very strong indicator.
If there's lot of hassle to set that sort of thing, don't worry much. Instead, go ahead and have all of these domains on one IP address and give the TLD give hint of what country it's in. It should work pretty well either way.No Need to Use Separate IP Address for Each Country-specific Site: Matt Cutts!,