fail to install-mbr to flash drive

I recently had to re-download Windows XP to another machine in the house.

This took time, it was frustrating!

When I finally got the set-up to start, the set-up asked me for Windows XP service pack 2.

I did not have the CD for that one.

I know I could download the SP2 on my laptap and I wanted to transfer the file to my flash/thumb drive.

First, I had to partition the flash drive.

Then, as I read, I had to install mbr to the flash drive.

This is where I met with a problem.

I type this in the terminal using a kubuntu 9.10 running on another computer but not fully-installed in the computer. Here are the commands:

ubuntu@ubuntu:~$ sudo su
root@ubuntu:/home/ubuntu# apt-get install mbr
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
  mbr
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 23.0kB of archives.
After this operation, 94.2kB of additional disk space will be used.
Get:1 http://archive.ubuntu.com karmic/main mbr 1.1.10-2 [23.0kB]
Fetched 23.0kB in 0s (32.6kB/s)
Selecting previously deselected package mbr.
(Reading database ... 90576 files and directories currently installed.)
Unpacking mbr (from .../archives/mbr_1.1.10-2_i386.deb) ...
Processing triggers for man-db ...
Setting up mbr (1.1.10-2) ...
root@ubuntu:/home/ubuntu# fdisk -l

That's where I ran into a problem. I don't know which file my flash/thumb drive is on.
Without inserting the flash drive into computer, this was the outcome of that last command.

root@ubuntu:/home/ubuntu# fdisk -l
Disk /dev/sda: 20.0 GB, 20020396032 bytes
240 heads, 63 sectors/track, 2586 cylinders
Units = cylinders of 15120 * 512 = 7741440 bytes
Disk identifier: 0xc70ac70a

   Device Boot Start End Blocks Id System
/dev/sda1 * 1 2585 19542568+ 7 HPFS/NTFS
root@ubuntu:/home/ubuntu#

With the flash/thumb drive inserted on the computer, this is what I found.

root@ubuntu:/home/ubuntu# fdisk -l
\
Disk /dev/sda: 20.0 GB, 20020396032 bytes
240 heads, 63 sectors/track, 2586 cylinders
Units = cylinders of 15120 * 512 = 7741440 bytes
Disk identifier: 0xc70ac70a

   Device Boot Start End Blocks Id System
/dev/sda1 * 1 2585 19542568+ 7 HPFS/NTFS

Disk /dev/sdb: 1029 MB, 1029701632 bytes
5 heads, 4 sectors/track, 100556 cylinders
Units = cylinders of 20 * 512 = 10240 bytes
Disk identifier: 0xfeba425d

   Device Boot Start End Blocks Id System
/dev/sdb1 4 97588 975840+ c W95 FAT32 (LBA)

Did I partition my drive wrong?

What letter will tell me which one is my thumb drive so I can hit:

install-mbr/dev/sdx (x replacing my drive) so I can install Windows XP Service pack 2 to my thumb drive through another program.

Please help, very lost and confused now.

Thank you!