I believe that Windows is installed on the second partition, but now I'm even unsure about that. I find it hard to understand why Windows would require four partitions.
Windows doesn't require 4 partitions. It works happily on one. I wouldn't be surprised by 1 windows partition and 1 recovery partition, but I'm surprised by two of each. Still, there may be a good reason.
It will work on one partition, yes, but by default, Windows 7 does install a 100MB recovery partition first, then the main OS in another. Then I suppose Compaq have added some weird OEM partitions in.. Maybe a partition for the Users folder or some such, keeping the installed programs and OS separate from the user data probably?? Could an extra partition which holds all the drivers for the machine or something bizarre like that.
Anyway, my vote/2p goes on the Wubi route or you could even run your Ubuntu install entirely inside a Virtual Machine which I am pretty sure I've seen discussed around 'ere before. Go for Wubi first, you've literally got nothing to lose. If you don't like it or it doesn't perform as well enough, uninstall it and it's gone. I've used Wubi once before ages ago and it was great at the time..
Handy thing with a Virtual Machine is you get dynamic hard drive size, the file which holds the "hard drive" can be as big as it takes up till it fills whatever partition it's in.
Cheers, Simon (p.s. I will be at pub tomorrow night.)