Long Story ... maybe it will help someone else in similar situation.
-started with Win7pro, added WinXP, added LMDE about a year ago
-had problems with sluggish performance, even after a fresh wipe and re-load; MB diags passed, Memtest86 passed, WD Disk Diagnostics passed, EVENTUALLY. Slower than predicted.
-reformatted, tried installing Mint xfce rather than LMDE Cinnamon, for perhaps better VirtualBox and/or VmWare success or even WINE, which has never provided me with any Windows apps (I'm running mostly boring old DOS/Windows games, rather than modern RPGs that PlayOnLinux offers).
-install failed, disk problems. Replaced WD hard drive with new Hitachi, hopefully better reliability.
-installed Mint 17.1 with xfce, manual partitioning, intentionally over-sized.
/boot - 512MB ext2
/swap - 16GB swap
/root - 40GB ext4
/tmp - 20GB ext4
/var - 20GB ext4
/home - huge ext4
/winXP - 20GB ntfs
/win7 - 20GB ntfs
-Mint install succeeds and boots
-try to install WinXp and/or Win7, which fail despite the NTFS partitions... I apparently left no recognizable boot space for them.
-use gparted live to re-size and move /boot to the right, with 100MB empty space preceding, then format the 100MB space to FAT32
-try to load Win7, fails; try to load WinXP, succeeds; try Win7 again, succeeds. Do Win7 updates, mostly succeeds. Reboot.
-No Linux, No WinXP, auto boot into Win7. Run BootRepair acquired from SourceForge, reboot, find Linux Mint, no Windows.
-run BootRepair trying different options, no joy. Still only Linux Mint.
-Search for help on adding windows to grub on linux mint, found this thread.
-saw the suggestion to "sudo os-prober" and "sudo update-grub" posted by oobetimer, and tried it.
Thank you oobetimer.