MY T41 is 14 inch 2374-7FU with 2GHz cpu and 1.5 GB memory and a slow hitachi 160GB HD ll: .I rarely use the cd/dvd drive or the pcmcia(?) slot.
How do I go about getting a sata hd in the cd slot.

Look up; you'll see an advertisement for newmodeus.com, who makes such UltraBay caddies.
Or you can get them very cheap on eBay if you're willing to wait for shipping from Hong Kong. I believe 3rd-party caddies for the T60/61 generation will work with your T41.

Any easy way to know if the offered caddy is for 14" T41?.

The (Ultrabay Slim) drivebays in a T6x and a T4x are all the same size.

UltraBay devices are standardized and exchangeable between different ThinkPad models.
http://www.thinkwiki.org/wiki/Ultrabay

An "UltraBay Slim" hard drive caddy, one designed for any of the following models, should work with your T41:
T40, T40p, T41, T41p, T42, T42p, T43, T43p, T60, T60p, T61, T61p, Z60t, Z61t, Z61p, X4 UltraBase, X4 Dock, X6 UltraBase, X6 Tablet UltraBase

... a small "correction" here which the OP might want to be aware of is about "The small tab at the end of the T60 UltraBay" as discussed in the thread [FS] Genuine Lenovo ultrabay slim hdd adapter FRU 26r9246 and more precisely in this post.

@ the OP: If you really want to speed up your T41, then the way to go is to get a SSD... see e.g the threads T42 SSD Conversion Success (1.8" SATA drive + bridge board) and 1.8" SATA to 2.5" IDE converter? and stay alert... those threads will be updated shortly with a lot of interesting news!

The idea of getting a (relatively cheap) 2.5" SATA SSD to work in the UltraBay of a T4x/p (which is your initial question) has been discussed e.g. in the threads How to use 2.5" SATA SSD as main boot drive for T42 and SATA hard drive caddy in ultrabay and Slow boot when using only ultrabay SATA HD in T42 and Empty primary bay causes boot timeout from SATA ultrabay (and in a related thread [R51]How to avoid boot delay if no main HDD is installed?) but in my case I'd rather like to get the 1.8" SATA SSD to work in the main HDD-bay for two reasons: 1) I would like to retain the internal CV/DVD, and 2) There is a significant boot delay (about 30 secs?!) if you boot from a HDD or a SDD in the Ultrabay, and I am not sure about whether there's a way to circumvent/avoid this delay?

PS: I am moving this thread to the T4x sub-forum, where it belongs.

Johan

Indeed, genuine Lenovo caddies have this limitation. I thought I specified "3rd-party caddies" in my post above, but apparently didn't.