Me to installed without any hassles on my Nokia 5700XM.
Do one thing go to Settings>Date & Time,
Then change the year to 2007,
Close the settings.
Launch the web browser,go to yahoo,click download & let it install.
This time you should not get Certificate error.
After it is installed change the year back to 2008 & then only start the yahoo go 3.0.
Remember : When you change the date & browse the net,the phone will give you untrusted certificate error.Plz accept them.They won't harm your phone in any way.
Ha Ha Ha.....Remember we must change date for installation for a old application (Generally old application gives "Certificate Expired" Error not "Certificate Error"), but Yahoo Go 3.0 is latest application released in early 2008.
Anyway problem is the same. I hv tried downloading it two times and spent Rs. 50/- at all.
Link provided by Naveen is invalid, I don't think so yahoo is distributing .sis file for S60 V3, Yahoo Go is still in .jar format.