Thank you all for your helpful comments and links.
In answer to Johan's question about my wants and needs, they're pretty basic. I'm not a power user, so my usage includes Office applications, Web browsing, watching videos on the Web. My current A30P with an ancient processor handles these tasks pretty well.
What seem like limited performance gains from a C2D processor over a Core Duo do not encourage me to go through the acrobatics involved in swapping a mobo etc. I have some experience working on my A30P. The screen went out once, and I bought a matching replacement UXGA screen from an A31P along with its inverter and cable. I never identified which component had failed (probably the inverter, which was buzzing before the screen went blank), so I replaced all three components.
But attaching the cable to the screen was one of the most excruciating mechanical exercises I've ever gone through. It took a couple of hours before I managed somehow to get the black plastic side clips in the connector to slide in properly. (The diagram in the HMM wasn't helpful.) So I'm unsure I have the patience to go through that exercise again to put a UXGA screen in a T60P C2D.
Meantime, my main concern with the T60P at this point is the noise.
In explanation, in November I bought a second-hand T60P w/ a T2600/2.13 GHz processor, 4GB of memory and a 320GB (but 5400 rpm) WD HDD. (Before the flooding in Thailand and before finding that T60P, I had bought a new Hitachi 320GB/7200 HDD, but have yet to install it.)
While I haven't installed Office etc. on the T60P, I'm very happy with its performance (it's good enough for my needs). And if I've posted here it's because I want a second T60P to network with the first and to have in the event I have problems with the first one, since I will retire the A30P, which I've had for 10 years. In particular, as a one-man consulting business, I need to both keep my life simple and enure reliability of my equipment.
The one for sale currently in my area (Paris) has the advantage of being at a reasonable price and geographically accessible. Plus I rarely see T60Ps with 15" screens for sale around Paris.
My main and only issue with my current T60P is the fan noise, which is s annoying but bearable. I vacuumed out the machine and checked for dust around the fan (I saw none), and have run the machine with and without a 2504 dock. (I bought the dock on eBay in order to have a DVI output to run two outboard screens, one with DVI the other with the VGA port.)
The fan comes on in two stages, but runs continuously after a few minutes of turning the machine on. The noise is the same with and without the dock. However, I want to see what I can do to fix it, knowing I've already updated the BIOS to the latest version.
I'd already read a number of threads about this problem, including those on using the temp-control software. I've noticed some people mention that the fan used in the C2D machines works better than the fan in the Core duo machines, and that they're interchangeable. In one thread I read: "41W6407 is a newer and improved version of 41V9932" and I also noted a thread saying 41W6407 was designed for Core 2 Duo machines and provides better cooling: viewtopic.php?f=29&t=89929
Thanks Johan for the German thread on replacing the T60 fan with another model. That sounds like a last but possible resort.
Both T60P and R500 fans are available for reasonable prices new on the IBM parts site.
While I haven't yet investigated the noise problem, I'll be getting to it soon, and will go through the many threads and try to decide the best way to get the noisy beast under control. More later.
Meantime, thank you Johan, too, for the suggestion about an SSD drive. I wonder if using an SSD drive will reduce the heat and make the machine run cooler and hopefully not make the fan turn on more often or run so fast. And I wasn't aware of the SATA interface limitation on the T60P
And thanks for the checklist. I had made one of my own for the first T60P, but a couple of points had escaped me. I've added them to my list for checking the T60P currently for sale in my area, which I plan to see in the next day or two.
All in all, I think a standard T60P, hopefully rejiggered to combat the noise, is the best compromise for my needs and with my patience for building a full-blown Frankenpad. I'd love to go that route, but I'm unsure the performance gains would be more important than slaying the noise dragon.
More comments welcome. Thanks for all the help so far!